Migrate HostZoomMap to live in StoragePartition.

This CL changes the persistence of host zoom levels to be on
a per-storage-partition basis, as opposed to (the current)
per-profile basis. This is needed to allow WebView content
(withing apps) to keep their zoom levels independent of those
in the main browser window.

BUG=335317

Review URL: https://codereview.chromium.org/393133002

Cr-Commit-Position: refs/heads/master@{#303841}

52 files changed, 507 insertions, 379 deletions

diff --git a/android_webview/browser/aw_browser_context.cc b/android_webview/browser/aw_browser_context.cc
index c386ad5..32148fc 100644
--- a/android_webview/browser/aw_browser_context.cc
+++ b/android_webview/browser/aw_browser_context.cc
@@ -222,6 +222,12 @@ void AwBrowserContext::CreateUserPrefServiceIfNecessary() {
   }
 }
 
+scoped_ptr<content::ZoomLevelDelegate>
+AwBrowserContext::CreateZoomLevelDelegate(
+    const base::FilePath& partition_path) {
+  return nullptr;
+}
+
 base::FilePath AwBrowserContext::GetPath() const {
   return context_storage_path_;
 }
diff --git a/android_webview/browser/aw_browser_context.h b/android_webview/browser/aw_browser_context.h
index 3f49765..0f2f278 100644
--- a/android_webview/browser/aw_browser_context.h
+++ b/android_webview/browser/aw_browser_context.h
@@ -93,6 +93,8 @@ class AwBrowserContext : public content::BrowserContext,
   void CreateUserPrefServiceIfNecessary();
 
   // content::BrowserContext implementation.
+  scoped_ptr<content::ZoomLevelDelegate> CreateZoomLevelDelegate(
+      const base::FilePath& partition_path) override;
   virtual base::FilePath GetPath() const override;
   virtual bool IsOffTheRecord() const override;
   virtual net::URLRequestContextGetter* GetRequestContext() override;
diff --git a/chrome/browser/browsing_data/browsing_data_remover_unittest.cc b/chrome/browser/browsing_data/browsing_data_remover_unittest.cc
index e8b895d..4a15378 100644
--- a/chrome/browser/browsing_data/browsing_data_remover_unittest.cc
+++ b/chrome/browser/browsing_data/browsing_data_remover_unittest.cc
@@ -152,6 +152,12 @@ class TestStoragePartition : public StoragePartition {
   }
   content::GeofencingManager* GetGeofencingManager() override { return NULL; }
 
+  content::HostZoomMap* GetHostZoomMap() override { return NULL; }
+  content::HostZoomLevelContext* GetHostZoomLevelContext() override {
+    return NULL;
+  }
+  content::ZoomLevelDelegate* GetZoomLevelDelegate() override { return NULL; }
+
   void ClearDataForOrigin(uint32 remove_mask,
                           uint32 quota_storage_remove_mask,
                           const GURL& storage_origin,
diff --git a/chrome/browser/profiles/host_zoom_map_browsertest.cc b/chrome/browser/profiles/host_zoom_map_browsertest.cc
index 15c32ce..cdb5bd6 100644
--- a/chrome/browser/profiles/host_zoom_map_browsertest.cc
+++ b/chrome/browser/profiles/host_zoom_map_browsertest.cc
@@ -19,6 +19,7 @@
 #include "base/values.h"
 #include "chrome/browser/chrome_page_zoom.h"
 #include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/profiles/profile_impl.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/tabs/tab_strip_model.h"
 #include "chrome/browser/ui/zoom/chrome_zoom_level_prefs.h"
@@ -35,6 +36,8 @@
 #include "testing/gmock/include/gmock/gmock.h"
 #include "url/gurl.h"
 
+using content::HostZoomMap;
+
 namespace {
 
 class ZoomLevelChangeObserver {
@@ -341,3 +344,58 @@ IN_PROC_BROWSER_TEST_F(HostZoomMapMigrationBrowserTest,
   EXPECT_EQ(0.0, profile_prefs->GetDouble(prefs::kDefaultZoomLevelDeprecated));
 }
 
+// Test four things:
+//  1. Host zoom maps of parent profile and child profile are different.
+//  2. Child host zoom map inherits zoom level at construction.
+//  3. Change of zoom level doesn't propagate from child to parent.
+//  4. Change of zoom level propagates from parent to child.
+IN_PROC_BROWSER_TEST_F(HostZoomMapBrowserTest,
+                       OffTheRecordProfileHostZoomMap) {
+  // Constants for test case.
+  const std::string host("example.com");
+  const double zoom_level_25 = 2.5;
+  const double zoom_level_30 = 3.0;
+  const double zoom_level_40 = 4.0;
+
+  Profile* parent_profile = browser()->profile();
+  Profile* child_profile =
+      static_cast<ProfileImpl*>(parent_profile)->GetOffTheRecordProfile();
+  HostZoomMap* parent_zoom_map =
+      HostZoomMap::GetDefaultForBrowserContext(parent_profile);
+  ASSERT_TRUE(parent_zoom_map);
+
+  parent_zoom_map->SetZoomLevelForHost(host, zoom_level_25);
+  ASSERT_EQ(parent_zoom_map->GetZoomLevelForHostAndScheme("http", host),
+      zoom_level_25);
+
+  // Prepare child host zoom map.
+  HostZoomMap* child_zoom_map =
+      HostZoomMap::GetDefaultForBrowserContext(child_profile);
+  ASSERT_TRUE(child_zoom_map);
+
+  // Verify.
+  EXPECT_NE(parent_zoom_map, child_zoom_map);
+
+  EXPECT_EQ(parent_zoom_map->GetZoomLevelForHostAndScheme("http", host),
+            child_zoom_map->GetZoomLevelForHostAndScheme("http", host)) <<
+                "Child must inherit from parent.";
+
+  child_zoom_map->SetZoomLevelForHost(host, zoom_level_30);
+  ASSERT_EQ(
+      child_zoom_map->GetZoomLevelForHostAndScheme("http", host),
+      zoom_level_30);
+
+  EXPECT_NE(parent_zoom_map->GetZoomLevelForHostAndScheme("http", host),
+            child_zoom_map->GetZoomLevelForHostAndScheme("http", host)) <<
+                "Child change must not propagate to parent.";
+
+  parent_zoom_map->SetZoomLevelForHost(host, zoom_level_40);
+  ASSERT_EQ(
+      parent_zoom_map->GetZoomLevelForHostAndScheme("http", host),
+      zoom_level_40);
+
+  EXPECT_EQ(parent_zoom_map->GetZoomLevelForHostAndScheme("http", host),
+            child_zoom_map->GetZoomLevelForHostAndScheme("http", host)) <<
+                "Parent change should propagate to child.";
+  base::RunLoop().RunUntilIdle();
+}
diff --git a/chrome/browser/profiles/off_the_record_profile_impl.cc b/chrome/browser/profiles/off_the_record_profile_impl.cc
index 3e6d872..fd0a7f9 100644
--- a/chrome/browser/profiles/off_the_record_profile_impl.cc
+++ b/chrome/browser/profiles/off_the_record_profile_impl.cc
@@ -142,7 +142,7 @@ void OffTheRecordProfileImpl::Init() {
   GetRequestContext();
 #endif  // defined(OS_CHROMEOS)
 
-  InitHostZoomMap();
+  TrackZoomLevelsFromParent();
 
 #if defined(ENABLE_PLUGINS)
   ChromePluginServiceFilter::GetInstance()->RegisterResourceContext(
@@ -198,15 +198,20 @@ void OffTheRecordProfileImpl::InitIoData() {
   io_data_.reset(new OffTheRecordProfileIOData::Handle(this));
 }
 
-void OffTheRecordProfileImpl::InitHostZoomMap() {
+void OffTheRecordProfileImpl::TrackZoomLevelsFromParent() {
+  DCHECK_NE(INCOGNITO_PROFILE, profile_->GetProfileType());
+
+  // Here we only want to use zoom levels stored in the main-context's default
+  // storage partition. We're not interested in zoom levels in special
+  // partitions, e.g. those used by WebViewGuests.
   HostZoomMap* host_zoom_map = HostZoomMap::GetDefaultForBrowserContext(this);
   HostZoomMap* parent_host_zoom_map =
       HostZoomMap::GetDefaultForBrowserContext(profile_);
   host_zoom_map->CopyFrom(parent_host_zoom_map);
-  // Observe parent's HZM change for propagating change of parent's
-  // change to this HZM.
-  zoom_subscription_ = parent_host_zoom_map->AddZoomLevelChangedCallback(
-      base::Bind(&OffTheRecordProfileImpl::OnZoomLevelChanged,
+  // Observe parent profile's HostZoomMap changes so they can also be applied
+  // to this profile's HostZoomMap.
+  track_zoom_subscription_ = parent_host_zoom_map->AddZoomLevelChangedCallback(
+      base::Bind(&OffTheRecordProfileImpl::OnParentZoomLevelChanged,
                  base::Unretained(this)));
 }
 
@@ -227,6 +232,12 @@ base::FilePath OffTheRecordProfileImpl::GetPath() const {
   return profile_->GetPath();
 }
 
+scoped_ptr<content::ZoomLevelDelegate>
+OffTheRecordProfileImpl::CreateZoomLevelDelegate(
+    const base::FilePath& partition_path) {
+  return nullptr;
+}
+
 scoped_refptr<base::SequencedTaskRunner>
 OffTheRecordProfileImpl::GetIOTaskRunner() {
   return profile_->GetIOTaskRunner();
@@ -513,7 +524,7 @@ Profile* Profile::CreateOffTheRecordProfile() {
   return profile;
 }
 
-void OffTheRecordProfileImpl::OnZoomLevelChanged(
+void OffTheRecordProfileImpl::OnParentZoomLevelChanged(
     const HostZoomMap::ZoomLevelChange& change) {
   HostZoomMap* host_zoom_map = HostZoomMap::GetDefaultForBrowserContext(this);
   switch (change.mode) {
diff --git a/chrome/browser/profiles/off_the_record_profile_impl.h b/chrome/browser/profiles/off_the_record_profile_impl.h
index 53e0621..fd7e778 100644
--- a/chrome/browser/profiles/off_the_record_profile_impl.h
+++ b/chrome/browser/profiles/off_the_record_profile_impl.h
@@ -84,6 +84,8 @@ class OffTheRecordProfileImpl : public Profile {
 
   // content::BrowserContext implementation:
   base::FilePath GetPath() const override;
+  scoped_ptr<content::ZoomLevelDelegate> CreateZoomLevelDelegate(
+      const base::FilePath& partition_path) override;
   scoped_refptr<base::SequencedTaskRunner> GetIOTaskRunner() override;
   bool IsOffTheRecord() const override;
   content::DownloadManagerDelegate* GetDownloadManagerDelegate() override;
@@ -103,16 +105,19 @@ class OffTheRecordProfileImpl : public Profile {
   content::SSLHostStateDelegate* GetSSLHostStateDelegate() override;
 
  private:
-  FRIEND_TEST_ALL_PREFIXES(OffTheRecordProfileImplTest, GetHostZoomMap);
   void InitIoData();
-  void InitHostZoomMap();
+
+  // Allows a profile to track changes in zoom levels in its parent profile.
+  void TrackZoomLevelsFromParent();
 
 #if defined(OS_ANDROID) || defined(OS_IOS)
   void UseSystemProxy();
 #endif  // defined(OS_ANDROID) || defined(OS_IOS)
 
-  void OnZoomLevelChanged(const content::HostZoomMap::ZoomLevelChange& change);
   PrefProxyConfigTracker* CreateProxyConfigTracker();
+  // Callback function for tracking parent's zoom level changes.
+  void OnParentZoomLevelChanged(
+      const content::HostZoomMap::ZoomLevelChange& change);
 
   // The real underlying profile.
   Profile* profile_;
@@ -120,6 +125,7 @@ class OffTheRecordProfileImpl : public Profile {
   // Weak pointer owned by |profile_|.
   PrefServiceSyncable* prefs_;
 
+  scoped_ptr<content::HostZoomMap::Subscription> track_zoom_subscription_;
   scoped_ptr<OffTheRecordProfileIOData::Handle> io_data_;
 
   // We use a non-persistent content settings map for OTR.
@@ -132,8 +138,6 @@ class OffTheRecordProfileImpl : public Profile {
 
   scoped_ptr<PrefProxyConfigTracker> pref_proxy_config_tracker_;
 
-  scoped_ptr<content::HostZoomMap::Subscription> zoom_subscription_;
-
   DISALLOW_COPY_AND_ASSIGN(OffTheRecordProfileImpl);
 };
 
diff --git a/chrome/browser/profiles/off_the_record_profile_impl_unittest.cc b/chrome/browser/profiles/off_the_record_profile_impl_unittest.cc
deleted file mode 100644
index 86184c2..0000000
--- a/chrome/browser/profiles/off_the_record_profile_impl_unittest.cc
+++ /dev/null
@@ -1,189 +0,0 @@
-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "chrome/browser/profiles/off_the_record_profile_impl.h"
-
-#include "base/prefs/pref_registry_simple.h"
-#include "base/prefs/pref_service.h"
-#include "base/prefs/scoped_user_pref_update.h"
-#include "base/run_loop.h"
-#include "chrome/browser/prefs/browser_prefs.h"
-#include "chrome/browser/ui/zoom/chrome_zoom_level_prefs.h"
-#include "chrome/common/pref_names.h"
-#include "chrome/test/base/browser_with_test_window_test.h"
-#include "chrome/test/base/testing_browser_process.h"
-#include "chrome/test/base/testing_io_thread_state.h"
-#include "chrome/test/base/testing_pref_service_syncable.h"
-#include "chrome/test/base/testing_profile.h"
-#include "chrome/test/base/testing_profile_manager.h"
-#include "content/public/browser/host_zoom_map.h"
-#include "content/public/common/page_zoom.h"
-#include "net/dns/mock_host_resolver.h"
-
-using content::HostZoomMap;
-
-namespace {
-
-class TestingProfileWithHostZoomMap : public TestingProfile {
- public:
-  TestingProfileWithHostZoomMap() {
-    HostZoomMap* host_zoom_map = HostZoomMap::GetDefaultForBrowserContext(this);
-    zoom_subscription_ = host_zoom_map->AddZoomLevelChangedCallback(
-        base::Bind(&TestingProfileWithHostZoomMap::OnZoomLevelChanged,
-                   base::Unretained(this)));
-    zoom_level_prefs_.reset(
-        new chrome::ChromeZoomLevelPrefs(GetPrefs(), GetPath()));
-    zoom_level_prefs_->InitPrefsAndCopyToHostZoomMap(GetPath(), host_zoom_map);
-  }
-
-  ~TestingProfileWithHostZoomMap() override {}
-
-  // Profile overrides:
-  PrefService* GetOffTheRecordPrefs() override { return GetPrefs(); }
-
- private:
-  void OnZoomLevelChanged(const HostZoomMap::ZoomLevelChange& change) {
-
-    if (change.mode != HostZoomMap::ZOOM_CHANGED_FOR_HOST)
-      return;
-
-    HostZoomMap* host_zoom_map = HostZoomMap::GetDefaultForBrowserContext(this);
-
-    double level = change.zoom_level;
-    std::string per_host_zoom_levels(prefs::kPartitionPerHostZoomLevels);
-    per_host_zoom_levels.append(".0");
-    DictionaryPrefUpdate update(GetPrefs(),
-                                prefs::kPartitionPerHostZoomLevels);
-    base::DictionaryValue* host_zoom_dictionary = update.Get();
-    if (content::ZoomValuesEqual(level, host_zoom_map->GetDefaultZoomLevel())) {
-      host_zoom_dictionary->RemoveWithoutPathExpansion(change.host, NULL);
-    } else {
-      host_zoom_dictionary->SetWithoutPathExpansion(
-          change.host, new base::FundamentalValue(level));
-    }
-  }
-
-  scoped_ptr<HostZoomMap::Subscription> zoom_subscription_;
-  scoped_ptr<chrome::ChromeZoomLevelPrefs> zoom_level_prefs_;
-
-  DISALLOW_COPY_AND_ASSIGN(TestingProfileWithHostZoomMap);
-};
-
-}  // namespace
-
-// We need to have a BrowserProcess in g_browser_process variable, since
-// OffTheRecordProfileImpl ctor uses it in
-// ProfileIOData::InitializeProfileParams.
-class OffTheRecordProfileImplTest : public BrowserWithTestWindowTest {
- protected:
-  OffTheRecordProfileImplTest() {}
-
-  ~OffTheRecordProfileImplTest() override {}
-
-  // testing::Test overrides:
-  void SetUp() override {
-    profile_manager_.reset(new TestingProfileManager(browser_process()));
-    ASSERT_TRUE(profile_manager_->SetUp());
-
-    testing_io_thread_state_.reset(new chrome::TestingIOThreadState());
-    testing_io_thread_state_->io_thread_state()->globals()->host_resolver.reset(
-        new net::MockHostResolver());
-
-    BrowserWithTestWindowTest::SetUp();
-  }
-
-  void TearDown() override {
-    BrowserWithTestWindowTest::TearDown();
-
-    testing_io_thread_state_.reset();
-
-    profile_manager_.reset();
-  }
-
-  // BrowserWithTestWindowTest overrides:
-  TestingProfile* CreateProfile() override {
-    return new TestingProfileWithHostZoomMap;
-  }
-
- private:
-  TestingBrowserProcess* browser_process() {
-    return TestingBrowserProcess::GetGlobal();
-  }
-
-  scoped_ptr<TestingProfileManager> profile_manager_;
-  scoped_ptr<chrome::TestingIOThreadState> testing_io_thread_state_;
-
-  DISALLOW_COPY_AND_ASSIGN(OffTheRecordProfileImplTest);
-};
-
-// Test four things:
-//  1. Host zoom maps of parent profile and child profile are different.
-//  2. Child host zoom map inherites zoom level at construction.
-//  3. Change of zoom level doesn't propagate from child to parent.
-//  4. Change of zoom level propagate from parent to child.
-TEST_F(OffTheRecordProfileImplTest, GetHostZoomMap) {
-  // Constants for test case.
-  const std::string host("example.com");
-  const double zoom_level_25 = 2.5;
-  const double zoom_level_30 = 3.0;
-  const double zoom_level_40 = 4.0;
-
-  // The TestingProfile from CreateProfile above is the parent.
-  TestingProfile* parent_profile = GetProfile();
-  ASSERT_TRUE(parent_profile);
-  ASSERT_TRUE(parent_profile->GetPrefs());
-  ASSERT_TRUE(parent_profile->GetOffTheRecordPrefs());
-
-  // Prepare parent host zoom map.
-  HostZoomMap* parent_zoom_map =
-      HostZoomMap::GetDefaultForBrowserContext(parent_profile);
-  ASSERT_TRUE(parent_zoom_map);
-
-  parent_zoom_map->SetZoomLevelForHost(host, zoom_level_25);
-  ASSERT_EQ(parent_zoom_map->GetZoomLevelForHostAndScheme("http", host),
-      zoom_level_25);
-
-  // TODO(yosin) We need to wait ProfileImpl::Observe done for
-  // OnZoomLevelChanged.
-
-  // Prepare an off the record profile owned by the parent profile.
-  parent_profile->SetOffTheRecordProfile(
-      scoped_ptr<Profile>(new OffTheRecordProfileImpl(parent_profile)));
-  OffTheRecordProfileImpl* child_profile =
-      static_cast<OffTheRecordProfileImpl*>(
-          parent_profile->GetOffTheRecordProfile());
-  child_profile->InitIoData();
-  child_profile->InitHostZoomMap();
-
-  // Prepare child host zoom map.
-  HostZoomMap* child_zoom_map =
-      HostZoomMap::GetDefaultForBrowserContext(child_profile);
-  ASSERT_TRUE(child_zoom_map);
-
-  // Verify.
-  EXPECT_NE(parent_zoom_map, child_zoom_map);
-
-  EXPECT_EQ(parent_zoom_map->GetZoomLevelForHostAndScheme("http", host),
-            child_zoom_map->GetZoomLevelForHostAndScheme("http", host)) <<
-                "Child must inherit from parent.";
-
-  child_zoom_map->SetZoomLevelForHost(host, zoom_level_30);
-  ASSERT_EQ(
-      child_zoom_map->GetZoomLevelForHostAndScheme("http", host),
-      zoom_level_30);
-
-  EXPECT_NE(parent_zoom_map->GetZoomLevelForHostAndScheme("http", host),
-            child_zoom_map->GetZoomLevelForHostAndScheme("http", host)) <<
-                "Child change must not propagate to parent.";
-
-  parent_zoom_map->SetZoomLevelForHost(host, zoom_level_40);
-  ASSERT_EQ(
-      parent_zoom_map->GetZoomLevelForHostAndScheme("http", host),
-      zoom_level_40);
-
-  EXPECT_EQ(parent_zoom_map->GetZoomLevelForHostAndScheme("http", host),
-            child_zoom_map->GetZoomLevelForHostAndScheme("http", host)) <<
-                "Parent change should propagate to child.";
-  base::RunLoop().RunUntilIdle();
-}
diff --git a/chrome/browser/profiles/profile.cc b/chrome/browser/profiles/profile.cc
index f57decd..ebe8fbb 100644
--- a/chrome/browser/profiles/profile.cc
+++ b/chrome/browser/profiles/profile.cc
@@ -17,8 +17,10 @@
 #include "components/data_reduction_proxy/core/browser/data_reduction_proxy_prefs.h"
 #include "components/pref_registry/pref_registry_syncable.h"
 #include "components/sync_driver/sync_prefs.h"
+#include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_source.h"
+#include "content/public/browser/storage_partition.h"
 #include "content/public/browser/web_contents.h"
 #include "content/public/browser/web_ui.h"
 
@@ -267,3 +269,9 @@ bool ProfileCompare::operator()(Profile* a, Profile* b) const {
     return false;
   return a->GetOriginalProfile() < b->GetOriginalProfile();
 }
+
+double Profile::GetDefaultZoomLevelForProfile() {
+  return GetDefaultStoragePartition(this)
+      ->GetHostZoomMap()
+      ->GetDefaultZoomLevel();
+}
diff --git a/chrome/browser/profiles/profile.h b/chrome/browser/profiles/profile.h
index dd74492..dfeb21c 100644
--- a/chrome/browser/profiles/profile.h
+++ b/chrome/browser/profiles/profile.h
@@ -395,6 +395,10 @@ class Profile : public content::BrowserContext {
   // Creates an OffTheRecordProfile which points to this Profile.
   Profile* CreateOffTheRecordProfile();
 
+  // Convenience method to retrieve the default zoom level for the default
+  // storage partition.
+  double GetDefaultZoomLevelForProfile();
+
  private:
   bool restored_last_session_;
 
diff --git a/chrome/browser/profiles/profile_impl.cc b/chrome/browser/profiles/profile_impl.cc
index 7425274..2c9c98e 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -95,7 +95,6 @@
 #include "components/user_prefs/user_prefs.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/dom_storage_context.h"
-#include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/storage_partition.h"
@@ -156,7 +155,6 @@ using base::TimeDelta;
 using base::UserMetricsAction;
 using content::BrowserThread;
 using content::DownloadManagerDelegate;
-using content::HostZoomMap;
 
 namespace {
 
@@ -632,8 +630,6 @@ void ProfileImpl::DoFinalInit() {
     session_cookie_mode = content::CookieStoreConfig::RESTORED_SESSION_COOKIES;
   }
 
-  InitHostZoomMap();
-
   base::Callback<void(bool)> data_reduction_proxy_unavailable;
   scoped_ptr<data_reduction_proxy::DataReductionProxyParams>
       data_reduction_proxy_params;
@@ -716,6 +712,9 @@ void ProfileImpl::DoFinalInit() {
   content::BrowserContext::GetDefaultStoragePartition(this)->
       GetDOMStorageContext()->SetSaveSessionStorageOnDisk();
 
+  // TODO(wjmaclean): Remove this. crbug.com/420643
+  chrome::MigrateProfileZoomLevelPrefs(this);
+
   // The DomDistillerViewerSource is not a normal WebUI so it must be registered
   // as a URLDataSource early.
   RegisterDomDistillerViewerSource(this);
@@ -757,17 +756,6 @@ void ProfileImpl::DoFinalInit() {
 #endif
 }
 
-void ProfileImpl::InitHostZoomMap() {
-  HostZoomMap* host_zoom_map = HostZoomMap::GetDefaultForBrowserContext(this);
-  DCHECK(!zoom_level_prefs_);
-  zoom_level_prefs_.reset(
-      new chrome::ChromeZoomLevelPrefs(prefs_.get(), GetPath()));
-  zoom_level_prefs_->InitPrefsAndCopyToHostZoomMap(GetPath(), host_zoom_map);
-
-  // TODO(wjmaclean): Remove this. crbug.com/420643
-  chrome::MigrateProfileZoomLevelPrefs(this);
-}
-
 base::FilePath ProfileImpl::last_selected_directory() {
   return GetPrefs()->GetFilePath(prefs::kSelectFileLastDirectory);
 }
@@ -830,6 +818,12 @@ Profile::ProfileType ProfileImpl::GetProfileType() const {
   return REGULAR_PROFILE;
 }
 
+scoped_ptr<content::ZoomLevelDelegate>
+ProfileImpl::CreateZoomLevelDelegate(const base::FilePath& partition_path) {
+  return make_scoped_ptr(
+      new chrome::ChromeZoomLevelPrefs(GetPrefs(), GetPath(), partition_path));
+}
+
 base::FilePath ProfileImpl::GetPath() const {
   return path_;
 }
@@ -987,7 +981,8 @@ PrefService* ProfileImpl::GetPrefs() {
 }
 
 chrome::ChromeZoomLevelPrefs* ProfileImpl::GetZoomLevelPrefs() {
-  return zoom_level_prefs_.get();
+  return static_cast<chrome::ChromeZoomLevelPrefs*>(
+      GetDefaultStoragePartition(this)->GetZoomLevelDelegate());
 }
 
 PrefService* ProfileImpl::GetOffTheRecordPrefs() {
diff --git a/chrome/browser/profiles/profile_impl.h b/chrome/browser/profiles/profile_impl.h
index 2ff686e..eca569e 100644
--- a/chrome/browser/profiles/profile_impl.h
+++ b/chrome/browser/profiles/profile_impl.h
@@ -76,6 +76,8 @@ class ProfileImpl : public Profile {
   static void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry);
 
   // content::BrowserContext implementation:
+  scoped_ptr<content::ZoomLevelDelegate> CreateZoomLevelDelegate(
+      const base::FilePath& partition_path) override;
   base::FilePath GetPath() const override;
   content::DownloadManagerDelegate* GetDownloadManagerDelegate() override;
   net::URLRequestContextGetter* GetRequestContext() override;
@@ -169,10 +171,6 @@ class ProfileImpl : public Profile {
   // Does final initialization. Should be called after prefs were loaded.
   void DoFinalInit();
 
-  // TODO(wjmaclean): Delete this once the HostZoomMap moves to
-  // StoragePartition.
-  void InitHostZoomMap();
-
   // Does final prefs initialization and calls Init().
   void OnPrefsLoaded(bool success);
 
@@ -235,10 +233,6 @@ class ProfileImpl : public Profile {
   scoped_refptr<user_prefs::PrefRegistrySyncable> pref_registry_;
   scoped_ptr<PrefServiceSyncable> prefs_;
   scoped_ptr<PrefServiceSyncable> otr_prefs_;
-  // TODO(wjmaclean): This is only here temporarily until HostZoomMap moves
-  // into StoragePartition, after which it will also move to StoragePartition.
-  // Must declare this here so it is destroyed before the profile prefs service.
-  scoped_ptr<chrome::ChromeZoomLevelPrefs> zoom_level_prefs_;
   ProfileImplIOData::Handle io_data_;
 #if defined(ENABLE_EXTENSIONS)
   scoped_refptr<ExtensionSpecialStoragePolicy>
diff --git a/chrome/browser/ui/app_list/test/fake_profile.cc b/chrome/browser/ui/app_list/test/fake_profile.cc
index 91f9e3e..98aa668 100644
--- a/chrome/browser/ui/app_list/test/fake_profile.cc
+++ b/chrome/browser/ui/app_list/test/fake_profile.cc
@@ -25,6 +25,11 @@ base::FilePath FakeProfile::GetPath() const {
   return path_;
 }
 
+scoped_ptr<content::ZoomLevelDelegate> FakeProfile::CreateZoomLevelDelegate(
+    const base::FilePath& partition_path) {
+  return nullptr;
+}
+
 bool FakeProfile::IsOffTheRecord() const {
   return false;
 }
diff --git a/chrome/browser/ui/app_list/test/fake_profile.h b/chrome/browser/ui/app_list/test/fake_profile.h
index 5053451..083cf6e 100644
--- a/chrome/browser/ui/app_list/test/fake_profile.h
+++ b/chrome/browser/ui/app_list/test/fake_profile.h
@@ -22,6 +22,7 @@ namespace content {
 class DownloadManagerDelegate;
 class ResourceContext;
 class SSLHostStateDelegate;
+class ZoomLevelDelegate;
 }
 
 class FakeProfile : public Profile {
@@ -33,6 +34,8 @@ class FakeProfile : public Profile {
   std::string GetProfileName() override;
   ProfileType GetProfileType() const override;
   base::FilePath GetPath() const override;
+  scoped_ptr<content::ZoomLevelDelegate> CreateZoomLevelDelegate(
+      const base::FilePath& partition_path) override;
   bool IsOffTheRecord() const override;
   content::DownloadManagerDelegate* GetDownloadManagerDelegate() override;
   net::URLRequestContextGetter* GetRequestContextForRenderProcess(
diff --git a/chrome/browser/ui/toolbar/wrench_menu_model.cc b/chrome/browser/ui/toolbar/wrench_menu_model.cc
index 4057b53..27f91c3 100644
--- a/chrome/browser/ui/toolbar/wrench_menu_model.cc
+++ b/chrome/browser/ui/toolbar/wrench_menu_model.cc
@@ -283,6 +283,9 @@ WrenchMenuModel::WrenchMenuModel(ui::AcceleratorProvider* provider,
   Build();
   UpdateZoomControls();
 
+  // By asking for the HostZoomMap via the BrowserContext, we get the map
+  // associated with the default storage partition, and not the one related
+  // to any specialized storage partitions, e.g. those used by WebViewGuests.
   content_zoom_subscription_ =
       content::HostZoomMap::GetDefaultForBrowserContext(browser->profile())
           ->AddZoomLevelChangedCallback(base::Bind(
diff --git a/chrome/browser/ui/views/toolbar/wrench_menu.cc b/chrome/browser/ui/views/toolbar/wrench_menu.cc
index 8c1d8d2..0af66b1 100644
--- a/chrome/browser/ui/views/toolbar/wrench_menu.cc
+++ b/chrome/browser/ui/views/toolbar/wrench_menu.cc
@@ -61,7 +61,6 @@
 #include "ui/views/widget/widget.h"
 
 using base::UserMetricsAction;
-using content::HostZoomMap;
 using content::WebContents;
 using ui::MenuModel;
 using views::CustomButton;
@@ -494,10 +493,12 @@ class WrenchMenu::ZoomView : public WrenchMenuView {
         decrement_button_(NULL),
         fullscreen_button_(NULL),
         zoom_label_width_(0) {
-    content_zoom_subscription_ = HostZoomMap::GetDefaultForBrowserContext(
-        menu->browser_->profile())->AddZoomLevelChangedCallback(
-            base::Bind(&WrenchMenu::ZoomView::OnZoomLevelChanged,
-                       base::Unretained(this)));
+    content_zoom_subscription_ =
+        content::HostZoomMap::GetDefaultForBrowserContext(
+            menu->browser_->profile())
+            ->AddZoomLevelChangedCallback(
+                base::Bind(&WrenchMenu::ZoomView::OnZoomLevelChanged,
+                           base::Unretained(this)));
 
     browser_zoom_subscription_ = ZoomEventManager::GetForBrowserContext(
         menu->browser_->profile())->AddZoomLevelChangedCallback(
@@ -634,7 +635,7 @@ class WrenchMenu::ZoomView : public WrenchMenuView {
   void WrenchMenuDestroyed() override { WrenchMenuView::WrenchMenuDestroyed(); }
 
  private:
-  void OnZoomLevelChanged(const HostZoomMap::ZoomLevelChange& change) {
+  void OnZoomLevelChanged(const content::HostZoomMap::ZoomLevelChange& change) {
     UpdateZoomControls();
   }
 
diff --git a/chrome/browser/ui/webui/options/content_settings_handler.cc b/chrome/browser/ui/webui/options/content_settings_handler.cc
index b4ef36b..b073fb3 100644
--- a/chrome/browser/ui/webui/options/content_settings_handler.cc
+++ b/chrome/browser/ui/webui/options/content_settings_handler.cc
@@ -490,12 +490,15 @@ void ContentSettingsHandler::InitializeHandler() {
           &ContentSettingsHandler::UpdateProtectedContentExceptionsButton,
           base::Unretained(this)));
 
-  content::HostZoomMap* host_zoom_map =
-      content::HostZoomMap::GetDefaultForBrowserContext(context);
+  // Here we only subscribe to the HostZoomMap for the default storage partition
+  // since we don't allow the user to manage the zoom levels for apps.
+  // We're only interested in zoom-levels that are persisted, since the user
+  // is given the opportunity to view/delete these in the content-settings page.
   host_zoom_map_subscription_ =
-      host_zoom_map->AddZoomLevelChangedCallback(
-          base::Bind(&ContentSettingsHandler::OnZoomLevelChanged,
-                     base::Unretained(this)));
+      content::HostZoomMap::GetDefaultForBrowserContext(context)
+          ->AddZoomLevelChangedCallback(
+              base::Bind(&ContentSettingsHandler::OnZoomLevelChanged,
+                         base::Unretained(this)));
 
   flash_settings_manager_.reset(new PepperFlashSettingsManager(this, context));
 
diff --git a/chrome/browser/ui/zoom/chrome_zoom_level_prefs.cc b/chrome/browser/ui/zoom/chrome_zoom_level_prefs.cc
index 4125794..28c1bdd 100644
--- a/chrome/browser/ui/zoom/chrome_zoom_level_prefs.cc
+++ b/chrome/browser/ui/zoom/chrome_zoom_level_prefs.cc
@@ -34,51 +34,24 @@ std::string GetHash(
 namespace chrome {
 
 ChromeZoomLevelPrefs::ChromeZoomLevelPrefs(PrefService* pref_service,
-                                           const base::FilePath& profile_path)
+                                           const base::FilePath& profile_path,
+                                           const base::FilePath& partition_path)
     : pref_service_(pref_service),
-      profile_path_(profile_path),
       host_zoom_map_(nullptr) {
   DCHECK(pref_service_);
-}
-
-ChromeZoomLevelPrefs::~ChromeZoomLevelPrefs() {
-}
 
-void ChromeZoomLevelPrefs::InitPrefsAndCopyToHostZoomMap(
-    const base::FilePath& partition_path,
-    content::HostZoomMap* host_zoom_map) {
   DCHECK(!partition_path.empty());
-  DCHECK((partition_path == profile_path_) ||
-         profile_path_.IsParent(partition_path));
-  // This init function must be called only once.
-  DCHECK(!host_zoom_map_);
-  DCHECK(host_zoom_map);
-  host_zoom_map_ = host_zoom_map;
-
+  DCHECK((partition_path == profile_path) ||
+         profile_path.IsParent(partition_path));
   // Create a partition_key string with no '.'s in it. For the default
   // StoragePartition, this string will always be "0".
   base::FilePath partition_relative_path;
-  profile_path_.AppendRelativePath(partition_path, &partition_relative_path);
+  profile_path.AppendRelativePath(partition_path, &partition_relative_path);
   partition_key_ = GetHash(partition_relative_path);
 
-  // Initialize the default zoom level.
-  host_zoom_map_->SetDefaultZoomLevel(GetDefaultZoomLevelPref());
+}
 
-  // Initialize the HostZoomMap with per-host zoom levels from the persisted
-  // zoom-level preference values.
-  const base::DictionaryValue* host_zoom_dictionaries =
-      pref_service_->GetDictionary(prefs::kPartitionPerHostZoomLevels);
-  const base::DictionaryValue* host_zoom_dictionary = nullptr;
-  if (host_zoom_dictionaries->GetDictionary(partition_key_,
-                                            &host_zoom_dictionary)) {
-    // Since we're calling this before setting up zoom_subscription_ below we
-    // don't need to worry that host_zoom_dictionary is indirectly affected
-    // by calls to HostZoomMap::SetZoomLevelForHost().
-    ExtractPerHostZoomLevels(host_zoom_dictionary,
-                             true /* sanitize_partition_host_zoom_levels */);
-  }
-  zoom_subscription_ = host_zoom_map_->AddZoomLevelChangedCallback(base::Bind(
-      &ChromeZoomLevelPrefs::OnZoomLevelChanged, base::Unretained(this)));
+ChromeZoomLevelPrefs::~ChromeZoomLevelPrefs() {
 }
 
 std::string ChromeZoomLevelPrefs::GetHashForTesting(
@@ -196,4 +169,31 @@ void ChromeZoomLevelPrefs::ExtractPerHostZoomLevels(
   }
 }
 
+void ChromeZoomLevelPrefs::InitHostZoomMap(
+    content::HostZoomMap* host_zoom_map) {
+  // This init function must be called only once.
+  DCHECK(!host_zoom_map_);
+  DCHECK(host_zoom_map);
+  host_zoom_map_ = host_zoom_map;
+
+  // Initialize the default zoom level.
+  host_zoom_map_->SetDefaultZoomLevel(GetDefaultZoomLevelPref());
+
+  // Initialize the HostZoomMap with per-host zoom levels from the persisted
+  // zoom-level preference values.
+  const base::DictionaryValue* host_zoom_dictionaries =
+      pref_service_->GetDictionary(prefs::kPartitionPerHostZoomLevels);
+  const base::DictionaryValue* host_zoom_dictionary = nullptr;
+  if (host_zoom_dictionaries->GetDictionary(partition_key_,
+                                            &host_zoom_dictionary)) {
+    // Since we're calling this before setting up zoom_subscription_ below we
+    // don't need to worry that host_zoom_dictionary is indirectly affected
+    // by calls to HostZoomMap::SetZoomLevelForHost().
+    ExtractPerHostZoomLevels(host_zoom_dictionary,
+                             true /* sanitize_partition_host_zoom_levels */);
+  }
+  zoom_subscription_ = host_zoom_map_->AddZoomLevelChangedCallback(base::Bind(
+      &ChromeZoomLevelPrefs::OnZoomLevelChanged, base::Unretained(this)));
+}
+
 }  // namespace chrome
diff --git a/chrome/browser/ui/zoom/chrome_zoom_level_prefs.h b/chrome/browser/ui/zoom/chrome_zoom_level_prefs.h
index ff0eb84..e08aa63 100644
--- a/chrome/browser/ui/zoom/chrome_zoom_level_prefs.h
+++ b/chrome/browser/ui/zoom/chrome_zoom_level_prefs.h
@@ -15,6 +15,7 @@
 #include "base/prefs/pref_service.h"
 #include "base/prefs/pref_store.h"
 #include "content/public/browser/host_zoom_map.h"
+#include "content/public/browser/zoom_level_delegate.h"
 
 namespace base {
 class DictionaryValue;
@@ -28,25 +29,22 @@ namespace chrome {
 // to the per-partition default zoom levels from chrome/ flow through this
 // class. Any changes to per-host levels are updated when HostZoomMap calls
 // OnZoomLevelChanged.
-class ChromeZoomLevelPrefs {
+class ChromeZoomLevelPrefs : public content::ZoomLevelDelegate {
  public:
   typedef base::CallbackList<void(void)>::Subscription
       DefaultZoomLevelSubscription;
 
-  // Initialize the pref_service and the profile_path via the constructor,
+  // Initialize the pref_service and the partition_key via the constructor,
   // as these concepts won't be available in the content base class
-  // (to be added later) which will define the InitPrefsAndCopyToHostZoomMap
-  // interface. |pref_service_| must outlive this class.
+  // ZoomLevelDelegate, which will define the InitHostZoomMap interface.
+  // |pref_service_| must outlive this class.
   ChromeZoomLevelPrefs(PrefService* pref_service,
-                       const base::FilePath& profile_path);
+                       const base::FilePath& profile_path,
+                       const base::FilePath& partition_path);
   virtual ~ChromeZoomLevelPrefs();
 
   static std::string GetHashForTesting(const base::FilePath& relative_path);
 
-  virtual void InitPrefsAndCopyToHostZoomMap(
-      const base::FilePath& partition_path,
-      content::HostZoomMap* host_zoom_map);
-
   void SetDefaultZoomLevelPref(double level);
   double GetDefaultZoomLevelPref() const;
   scoped_ptr<DefaultZoomLevelSubscription> RegisterDefaultZoomLevelCallback(
@@ -56,6 +54,9 @@ class ChromeZoomLevelPrefs {
       const base::DictionaryValue* host_zoom_dictionary,
       bool sanitize_partition_host_zoom_levels);
 
+  // content::ZoomLevelDelegate
+  void InitHostZoomMap(content::HostZoomMap* host_zoom_map) override;
+
  private:
   // This is a callback function that receives notifications from HostZoomMap
   // when per-host zoom levels change. It is used to update the per-host
@@ -63,7 +64,6 @@ class ChromeZoomLevelPrefs {
   void OnZoomLevelChanged(const content::HostZoomMap::ZoomLevelChange& change);
 
   PrefService* pref_service_;
-  const base::FilePath profile_path_;
   content::HostZoomMap* host_zoom_map_;
   scoped_ptr<content::HostZoomMap::Subscription> zoom_subscription_;
   std::string partition_key_;
diff --git a/chrome/browser/ui/zoom/zoom_controller.cc b/chrome/browser/ui/zoom/zoom_controller.cc
index a9b7029..1918ce5 100644
--- a/chrome/browser/ui/zoom/zoom_controller.cc
+++ b/chrome/browser/ui/zoom/zoom_controller.cc
@@ -27,10 +27,8 @@ ZoomController::ZoomController(content::WebContents* web_contents)
       zoom_mode_(ZOOM_MODE_DEFAULT),
       zoom_level_(1.0),
       browser_context_(web_contents->GetBrowserContext()) {
-  // TODO(wjmaclean) Make calls to HostZoomMap::GetDefaultForBrowserContext()
-  // refer to the webcontents-specific HostZoomMap when that becomes available.
   content::HostZoomMap* host_zoom_map =
-      content::HostZoomMap::GetDefaultForBrowserContext(browser_context_);
+      content::HostZoomMap::GetForWebContents(web_contents);
   zoom_level_ = host_zoom_map->GetDefaultZoomLevel();
 
   zoom_subscription_ = host_zoom_map->AddZoomLevelChangedCallback(
@@ -118,7 +116,7 @@ bool ZoomController::SetZoomLevelByExtension(
   }
 
   content::HostZoomMap* zoom_map =
-      content::HostZoomMap::GetDefaultForBrowserContext(browser_context_);
+      content::HostZoomMap::GetForWebContents(web_contents());
   DCHECK(zoom_map);
   DCHECK(!event_data_);
   event_data_.reset(new ZoomChangedEventData(web_contents(),
@@ -152,7 +150,7 @@ void ZoomController::SetZoomMode(ZoomMode new_mode) {
     return;
 
   content::HostZoomMap* zoom_map =
-      content::HostZoomMap::GetDefaultForBrowserContext(browser_context_);
+      content::HostZoomMap::GetForWebContents(web_contents());
   DCHECK(zoom_map);
   int render_process_id = web_contents()->GetRenderProcessHost()->GetID();
   int render_view_id = web_contents()->GetRenderViewHost()->GetRoutingID();
diff --git a/chrome/browser/ui/zoom/zoom_controller.h b/chrome/browser/ui/zoom/zoom_controller.h
index db771ee..7dad4ad 100644
--- a/chrome/browser/ui/zoom/zoom_controller.h
+++ b/chrome/browser/ui/zoom/zoom_controller.h
@@ -73,10 +73,8 @@ class ZoomController : public content::WebContentsObserver,
   // Convenience method to get default zoom level. Implemented here for
   // inlining.
   double GetDefaultZoomLevel() const {
-    // TODO(wjmaclean) Make this refer to the webcontents-specific HostZoomMap
-    // when that becomes available.
-    return content::HostZoomMap::GetDefaultForBrowserContext(browser_context_)->
-        GetDefaultZoomLevel();
+    return content::HostZoomMap::GetForWebContents(web_contents())
+        ->GetDefaultZoomLevel();
   }
 
   // Convenience method to quickly check if the tab's at default zoom.
diff --git a/chrome/browser/ui/zoom/zoom_controller_browsertest.cc b/chrome/browser/ui/zoom/zoom_controller_browsertest.cc
index 36a2114..4d0ffd5 100644
--- a/chrome/browser/ui/zoom/zoom_controller_browsertest.cc
+++ b/chrome/browser/ui/zoom/zoom_controller_browsertest.cc
@@ -20,8 +20,6 @@
 #include "content/public/test/browser_test_utils.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
-typedef InProcessBrowserTest ZoomControllerBrowserTest;
-
 bool operator==(const ZoomController::ZoomChangedEventData& lhs,
                 const ZoomController::ZoomChangedEventData& rhs) {
   return lhs.web_contents == rhs.web_contents &&
@@ -59,7 +57,17 @@ class ZoomChangedWatcher : public ZoomObserver {
   DISALLOW_COPY_AND_ASSIGN(ZoomChangedWatcher);
 };
 
-// TODO(wjmaclean): Enable this on Android when we can kill the process there.
+class TestZoomObserver : public ZoomObserver {
+ public:
+  MOCK_METHOD1(OnZoomChanged,
+               void(const ZoomController::ZoomChangedEventData&));
+};
+
+class ZoomControllerBrowserTest: public InProcessBrowserTest {
+ protected:
+  TestZoomObserver zoom_observer_;
+};
+
 #if defined(OS_ANDROID)
 #define MAYBE_CrashedTabsDoNotChangeZoom DISABLED_CrashedTabsDoNotChangeZoom
 #else
@@ -133,3 +141,28 @@ IN_PROC_BROWSER_TEST_F(ZoomControllerBrowserTest, ErrorPagesCanZoom) {
   zoom_controller->SetZoomLevel(new_zoom_level);
   EXPECT_FLOAT_EQ(new_zoom_level, zoom_controller->GetZoomLevel());
 }
+
+IN_PROC_BROWSER_TEST_F(ZoomControllerBrowserTest, Observe) {
+  content::WebContents* web_contents =
+      browser()->tab_strip_model()->GetActiveWebContents();
+  ZoomController* zoom_controller =
+      ZoomController::FromWebContents(web_contents);
+  zoom_controller->AddObserver(&zoom_observer_);
+
+  double new_zoom_level = 1.0;
+  // When the event is initiated from HostZoomMap, the old zoom level is not
+  // available.
+  ZoomController::ZoomChangedEventData zoom_change_data(
+      web_contents,
+      new_zoom_level,
+      new_zoom_level,
+      ZoomController::ZOOM_MODE_DEFAULT,
+      true);  // We have a non-empty host, so this will be 'true'.
+  EXPECT_CALL(zoom_observer_, OnZoomChanged(zoom_change_data)).Times(1);
+
+  content::HostZoomMap* host_zoom_map =
+      content::HostZoomMap::GetDefaultForBrowserContext(
+          web_contents->GetBrowserContext());
+
+  host_zoom_map->SetZoomLevelForHost("about:blank", new_zoom_level);
+}
diff --git a/chrome/browser/ui/zoom/zoom_controller_unittest.cc b/chrome/browser/ui/zoom/zoom_controller_unittest.cc
index 1d468f9..2db242f 100644
--- a/chrome/browser/ui/zoom/zoom_controller_unittest.cc
+++ b/chrome/browser/ui/zoom/zoom_controller_unittest.cc
@@ -70,25 +70,6 @@ TEST_F(ZoomControllerTest, DidNavigateMainFrame) {
                                          content::FrameNavigateParams());
 }
 
-TEST_F(ZoomControllerTest, Observe) {
-  double new_zoom_level = 110.0;
-  // When the event is initiated from HostZoomMap, the old zoom level is not
-  // available.
-  ZoomController::ZoomChangedEventData zoom_change_data(
-      web_contents(),
-      new_zoom_level,
-      new_zoom_level,
-      ZoomController::ZOOM_MODE_DEFAULT,
-      false);
-  EXPECT_CALL(zoom_observer_, OnZoomChanged(zoom_change_data)).Times(1);
-
-  content::HostZoomMap* host_zoom_map =
-      content::HostZoomMap::GetDefaultForBrowserContext(
-          web_contents()->GetBrowserContext());
-
-  host_zoom_map->SetZoomLevelForHost(std::string(), new_zoom_level);
-}
-
 TEST_F(ZoomControllerTest, Observe_ZoomController) {
   double old_zoom_level = zoom_controller_->GetZoomLevel();
   double new_zoom_level = 110.0;
diff --git a/chrome/chrome_tests_unit.gypi b/chrome/chrome_tests_unit.gypi
index 643f404..07e776e 100644
--- a/chrome/chrome_tests_unit.gypi
+++ b/chrome/chrome_tests_unit.gypi
@@ -628,7 +628,6 @@
       'browser/profiles/file_path_verifier_win_unittest.cc',
       'browser/profiles/gaia_info_update_service_unittest.cc',
       'browser/profiles/incognito_mode_policy_handler_unittest.cc',
-      'browser/profiles/off_the_record_profile_impl_unittest.cc',
       'browser/profiles/profile_downloader_unittest.cc',
       'browser/profiles/profile_info_cache_unittest.cc',
       'browser/profiles/profile_info_cache_unittest.h',
@@ -2587,7 +2586,6 @@
             'browser/font_family_cache_unittest.cc',
             'browser/policy/policy_path_parser_unittest.cc',
             'browser/process_singleton_posix_unittest.cc',
-            'browser/profiles/off_the_record_profile_impl_unittest.cc',
             'browser/profiles/profile_list_desktop_unittest.cc',
             'browser/power/process_power_collector_unittest.cc',
             'browser/renderer_context_menu/render_view_context_menu_unittest.cc',
diff --git a/chrome/test/base/testing_profile.cc b/chrome/test/base/testing_profile.cc
index 5588f656..2f540ca 100644
--- a/chrome/test/base/testing_profile.cc
+++ b/chrome/test/base/testing_profile.cc
@@ -634,6 +634,11 @@ base::FilePath TestingProfile::GetPath() const {
   return profile_path_;
 }
 
+scoped_ptr<content::ZoomLevelDelegate> TestingProfile::CreateZoomLevelDelegate(
+    const base::FilePath& partition_path) {
+  return nullptr;
+}
+
 scoped_refptr<base::SequencedTaskRunner> TestingProfile::GetIOTaskRunner() {
   return base::MessageLoop::current()->message_loop_proxy();
 }
diff --git a/chrome/test/base/testing_profile.h b/chrome/test/base/testing_profile.h
index df2c135..274f6c42 100644
--- a/chrome/test/base/testing_profile.h
+++ b/chrome/test/base/testing_profile.h
@@ -17,6 +17,7 @@
 namespace content {
 class MockResourceContext;
 class SSLHostStateDelegate;
+class ZoomLevelDelegate;
 }
 
 namespace history {
@@ -221,6 +222,8 @@ class TestingProfile : public Profile {
 
   // content::BrowserContext
   base::FilePath GetPath() const override;
+  scoped_ptr<content::ZoomLevelDelegate> CreateZoomLevelDelegate(
+      const base::FilePath& partition_path) override;
   scoped_refptr<base::SequencedTaskRunner> GetIOTaskRunner() override;
   bool IsOffTheRecord() const override;
   content::DownloadManagerDelegate* GetDownloadManagerDelegate() override;
diff --git a/content/browser/download/download_manager_impl_unittest.cc b/content/browser/download/download_manager_impl_unittest.cc
index 0c5eb52..fc43b2c 100644
--- a/content/browser/download/download_manager_impl_unittest.cc
+++ b/content/browser/download/download_manager_impl_unittest.cc
@@ -28,6 +28,7 @@
 #include "content/public/browser/download_interrupt_reasons.h"
 #include "content/public/browser/download_item.h"
 #include "content/public/browser/download_manager_delegate.h"
+#include "content/public/browser/zoom_level_delegate.h"
 #include "content/public/test/mock_download_item.h"
 #include "content/public/test/test_browser_context.h"
 #include "content/public/test/test_browser_thread.h"
@@ -53,6 +54,16 @@ ACTION_TEMPLATE(RunCallback,
   return ::std::tr1::get<k>(args).Run(p0);
 }
 
+// Create a specialization so we can mock an override for
+// scoped_ptr<content::ZoomLevelDelegate>
+// BrowserContext::CreateZoomLevelDelegate(const base::FilePath&).
+template<>
+class scoped_ptr<content::ZoomLevelDelegate> {
+ public:
+  scoped_ptr() {}
+  ~scoped_ptr() {}
+};
+
 namespace content {
 class ByteStreamReader;
 
@@ -401,6 +412,8 @@ class MockBrowserContext : public BrowserContext {
   ~MockBrowserContext() {}
 
   MOCK_CONST_METHOD0(GetPath, base::FilePath());
+  MOCK_METHOD1(CreateZoomLevelDelegate,
+               scoped_ptr<ZoomLevelDelegate>(const base::FilePath&));
   MOCK_CONST_METHOD0(IsOffTheRecord, bool());
   MOCK_METHOD0(GetRequestContext, net::URLRequestContextGetter*());
   MOCK_METHOD1(GetRequestContextForRenderProcess,
diff --git a/content/browser/host_zoom_level_context.cc b/content/browser/host_zoom_level_context.cc
new file mode 100644
index 0000000..02ddcf5
--- /dev/null
+++ b/content/browser/host_zoom_level_context.cc
@@ -0,0 +1,32 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/host_zoom_level_context.h"
+
+#include "base/files/file_path.h"
+#include "content/browser/host_zoom_map_impl.h"
+#include "content/public/browser/browser_thread.h"
+
+namespace content {
+
+HostZoomLevelContext::HostZoomLevelContext(
+    scoped_ptr<ZoomLevelDelegate> zoom_level_delegate)
+    : host_zoom_map_impl_(new HostZoomMapImpl()),
+      zoom_level_delegate_(zoom_level_delegate.Pass()) {
+  if (zoom_level_delegate_)
+    zoom_level_delegate_->InitHostZoomMap(host_zoom_map_impl_.get());
+}
+
+HostZoomLevelContext::~HostZoomLevelContext() {}
+
+void HostZoomLevelContext::DeleteOnCorrectThread() const {
+  if (BrowserThread::IsMessageLoopValid(BrowserThread::UI) &&
+      !BrowserThread::CurrentlyOn(BrowserThread::UI)) {
+    BrowserThread::DeleteSoon(BrowserThread::UI, FROM_HERE, this);
+    return;
+  }
+  delete this;
+}
+
+}  // namespace content
diff --git a/content/browser/host_zoom_level_context.h b/content/browser/host_zoom_level_context.h
new file mode 100644
index 0000000..e45222f
--- /dev/null
+++ b/content/browser/host_zoom_level_context.h
@@ -0,0 +1,61 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_BROWSER_HOST_ZOOM_LEVEL_CONTEXT_H_
+#define CONTENT_BROWSER_HOST_ZOOM_LEVEL_CONTEXT_H_
+
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/scoped_ptr.h"
+#include "content/browser/host_zoom_map_impl.h"
+#include "content/public/browser/zoom_level_delegate.h"
+
+class PrefService;
+
+namespace content {
+struct HostZoomLevelContextDeleter;
+
+// This class manages a HostZoomMap and associates it with a ZoomLevelDelegate,
+// if one is provided. It also serves to keep the zoom level machinery details
+// separate from the owning StoragePartitionImpl.
+class HostZoomLevelContext
+    : public base::RefCountedThreadSafe<HostZoomLevelContext,
+                                        HostZoomLevelContextDeleter> {
+ public:
+  explicit HostZoomLevelContext(
+      scoped_ptr<ZoomLevelDelegate> zoom_level_delegate);
+
+  HostZoomMap* GetHostZoomMap() const { return host_zoom_map_impl_.get(); }
+  ZoomLevelDelegate* GetZoomLevelDelegate() const {
+    return zoom_level_delegate_.get();
+  }
+
+ protected:
+  virtual ~HostZoomLevelContext();
+
+ private:
+  friend class base::DeleteHelper<HostZoomLevelContext>;
+  friend class base::RefCountedThreadSafe<HostZoomLevelContext,
+                                          HostZoomLevelContextDeleter>;
+  friend struct HostZoomLevelContextDeleter;
+
+  void DeleteOnCorrectThread() const;
+
+  scoped_ptr<HostZoomMapImpl> host_zoom_map_impl_;
+  // Release the delegate before the HostZoomMap, in case it is carrying
+  // any HostZoomMap::Subscription pointers.
+  scoped_ptr<ZoomLevelDelegate> zoom_level_delegate_;
+
+  DISALLOW_COPY_AND_ASSIGN(HostZoomLevelContext);
+};
+
+struct HostZoomLevelContextDeleter {
+  static void Destruct(const HostZoomLevelContext* context) {
+    context->DeleteOnCorrectThread();
+  }
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_HOST_ZOOM_LEVEL_CONTEXT_H_
diff --git a/content/browser/host_zoom_map_impl.cc b/content/browser/host_zoom_map_impl.cc
index 81f8182..b6595b9 100644
--- a/content/browser/host_zoom_map_impl.cc
+++ b/content/browser/host_zoom_map_impl.cc
@@ -20,6 +20,8 @@
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/resource_context.h"
+#include "content/public/browser/site_instance.h"
+#include "content/public/browser/storage_partition.h"
 #include "content/public/common/page_zoom.h"
 #include "content/public/common/url_constants.h"
 #include "net/base/net_util.h"
@@ -28,8 +30,6 @@ namespace content {
 
 namespace {
 
-const char kHostZoomMapKeyName[] = "content_host_zoom_map";
-
 std::string GetHostFromProcessView(int render_process_id, int render_view_id) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   RenderViewHost* render_view_host =
@@ -61,29 +61,39 @@ GURL HostZoomMap::GetURLFromEntry(const NavigationEntry* entry) {
 }
 
 HostZoomMap* HostZoomMap::GetDefaultForBrowserContext(BrowserContext* context) {
-  HostZoomMapImpl* rv = static_cast<HostZoomMapImpl*>(
-      context->GetUserData(kHostZoomMapKeyName));
-  if (!rv) {
-    rv = new HostZoomMapImpl();
-    context->SetUserData(kHostZoomMapKeyName, rv);
-  }
-  return rv;
+  StoragePartition* partition =
+      BrowserContext::GetDefaultStoragePartition(context);
+  DCHECK(partition);
+  return partition->GetHostZoomMap();
+}
+
+HostZoomMap* HostZoomMap::Get(SiteInstance* instance) {
+  StoragePartition* partition = BrowserContext::GetStoragePartition(
+      instance->GetBrowserContext(), instance);
+  DCHECK(partition);
+  return partition->GetHostZoomMap();
+}
+
+HostZoomMap* HostZoomMap::GetForWebContents(const WebContents* contents) {
+  StoragePartition* partition =
+      BrowserContext::GetStoragePartition(contents->GetBrowserContext(),
+                                          contents->GetSiteInstance());
+  DCHECK(partition);
+  return partition->GetHostZoomMap();
 }
 
 // Helper function for setting/getting zoom levels for WebContents without
 // having to import HostZoomMapImpl everywhere.
 double HostZoomMap::GetZoomLevel(const WebContents* web_contents) {
-  HostZoomMapImpl* host_zoom_map =
-      static_cast<HostZoomMapImpl*>(HostZoomMap::GetDefaultForBrowserContext(
-          web_contents->GetBrowserContext()));
+  HostZoomMapImpl* host_zoom_map = static_cast<HostZoomMapImpl*>(
+      HostZoomMap::GetForWebContents(web_contents));
   return host_zoom_map->GetZoomLevelForWebContents(
       *static_cast<const WebContentsImpl*>(web_contents));
 }
 
 void HostZoomMap::SetZoomLevel(const WebContents* web_contents, double level) {
-  HostZoomMapImpl* host_zoom_map =
-      static_cast<HostZoomMapImpl*>(HostZoomMap::GetDefaultForBrowserContext(
-          web_contents->GetBrowserContext()));
+  HostZoomMapImpl* host_zoom_map = static_cast<HostZoomMapImpl*>(
+      HostZoomMap::GetForWebContents(web_contents));
   host_zoom_map->SetZoomLevelForWebContents(
       *static_cast<const WebContentsImpl*>(web_contents), level);
 }
@@ -243,10 +253,12 @@ void HostZoomMapImpl::SetZoomLevelForHostAndScheme(const std::string& scheme,
 }
 
 double HostZoomMapImpl::GetDefaultZoomLevel() const {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   return default_zoom_level_;
 }
 
 void HostZoomMapImpl::SetDefaultZoomLevel(double level) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   default_zoom_level_ = level;
 }
 
@@ -396,8 +408,10 @@ void HostZoomMapImpl::SendZoomLevelChange(const std::string& scheme,
   for (RenderProcessHost::iterator i(RenderProcessHost::AllHostsIterator());
        !i.IsAtEnd(); i.Advance()) {
     RenderProcessHost* render_process_host = i.GetCurrentValue();
-    if (HostZoomMap::GetDefaultForBrowserContext(
-            render_process_host->GetBrowserContext()) == this) {
+    // TODO(wjmaclean) This will need to be cleaned up when
+    // RenderProcessHost::GetStoragePartition() goes away. Perhaps have
+    // RenderProcessHost expose a GetHostZoomMap() function?
+    if (render_process_host->GetStoragePartition()->GetHostZoomMap() == this) {
       render_process_host->Send(
           new ViewMsg_SetZoomLevelForCurrentURL(scheme, host, level));
     }
@@ -413,6 +427,7 @@ void HostZoomMapImpl::SendErrorPageZoomLevelRefresh() {
 }
 
 HostZoomMapImpl::~HostZoomMapImpl() {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 }
 
 }  // namespace content
diff --git a/content/browser/host_zoom_map_impl.h b/content/browser/host_zoom_map_impl.h
index 78d643d..f900287 100644
--- a/content/browser/host_zoom_map_impl.h
+++ b/content/browser/host_zoom_map_impl.h
@@ -11,7 +11,6 @@
 
 #include "base/compiler_specific.h"
 #include "base/sequenced_task_runner_helpers.h"
-#include "base/supports_user_data.h"
 #include "base/synchronization/lock.h"
 #include "content/public/browser/host_zoom_map.h"
 #include "content/public/browser/notification_observer.h"
@@ -24,8 +23,7 @@ class WebContentsImpl;
 // HostZoomMap needs to be deleted on the UI thread because it listens
 // to notifications on there (and holds a NotificationRegistrar).
 class CONTENT_EXPORT HostZoomMapImpl : public NON_EXPORTED_BASE(HostZoomMap),
-                                       public NotificationObserver,
-                                       public base::SupportsUserData::Data {
+                                       public NotificationObserver {
  public:
   HostZoomMapImpl();
   ~HostZoomMapImpl() override;
diff --git a/content/browser/loader/async_resource_handler.cc b/content/browser/loader/async_resource_handler.cc
index 5125bec..51b0a744 100644
--- a/content/browser/loader/async_resource_handler.cc
+++ b/content/browser/loader/async_resource_handler.cc
@@ -193,8 +193,7 @@ bool AsyncResourceHandler::OnResponseStarted(ResourceResponse* response,
 
   DevToolsNetLogObserver::PopulateResponseInfo(request(), response);
 
-  HostZoomMap* host_zoom_map =
-      GetHostZoomMapForResourceContext(info->GetContext());
+  const HostZoomMap* host_zoom_map = info->filter()->GetHostZoomMap();
 
   if (info->GetResourceType() == RESOURCE_TYPE_MAIN_FRAME && host_zoom_map) {
     const GURL& request_url = request()->url();
diff --git a/content/browser/loader/resource_dispatcher_host_unittest.cc b/content/browser/loader/resource_dispatcher_host_unittest.cc
index d18facd..3017086 100644
--- a/content/browser/loader/resource_dispatcher_host_unittest.cc
+++ b/content/browser/loader/resource_dispatcher_host_unittest.cc
@@ -210,7 +210,7 @@ class TestFilter : public ResourceMessageFilter {
   explicit TestFilter(ResourceContext* resource_context)
       : ResourceMessageFilter(
             ChildProcessHostImpl::GenerateChildProcessUniqueId(),
-            PROCESS_TYPE_RENDERER, NULL, NULL, NULL, NULL,
+            PROCESS_TYPE_RENDERER, NULL, NULL, NULL, NULL, NULL,
             base::Bind(&TestFilter::GetContexts, base::Unretained(this))),
         resource_context_(resource_context),
         canceled_(false),
diff --git a/content/browser/loader/resource_message_filter.cc b/content/browser/loader/resource_message_filter.cc
index 9ffa29f..4a20d9a 100644
--- a/content/browser/loader/resource_message_filter.cc
+++ b/content/browser/loader/resource_message_filter.cc
@@ -6,6 +6,7 @@
 
 #include "content/browser/appcache/chrome_appcache_service.h"
 #include "content/browser/fileapi/chrome_blob_storage_context.h"
+#include "content/browser/host_zoom_level_context.h"
 #include "content/browser/loader/resource_dispatcher_host_impl.h"
 #include "content/browser/service_worker/service_worker_context_wrapper.h"
 #include "content/common/resource_messages.h"
@@ -21,6 +22,7 @@ ResourceMessageFilter::ResourceMessageFilter(
     ChromeBlobStorageContext* blob_storage_context,
     storage::FileSystemContext* file_system_context,
     ServiceWorkerContextWrapper* service_worker_context,
+    HostZoomLevelContext* host_zoom_level_context,
     const GetContextsCallback& get_contexts_callback)
     : BrowserMessageFilter(ResourceMsgStart),
       child_id_(child_id),
@@ -29,6 +31,7 @@ ResourceMessageFilter::ResourceMessageFilter(
       blob_storage_context_(blob_storage_context),
       file_system_context_(file_system_context),
       service_worker_context_(service_worker_context),
+      host_zoom_level_context_(host_zoom_level_context),
       get_contexts_callback_(get_contexts_callback),
       weak_ptr_factory_(this) {
 }
@@ -53,6 +56,12 @@ void ResourceMessageFilter::GetContexts(
   return get_contexts_callback_.Run(request, resource_context, request_context);
 }
 
+const HostZoomMap* ResourceMessageFilter::GetHostZoomMap() const {
+  if (host_zoom_level_context_.get())
+    return host_zoom_level_context_->GetHostZoomMap();
+  return NULL;
+}
+
 base::WeakPtr<ResourceMessageFilter> ResourceMessageFilter::GetWeakPtr() {
   return weak_ptr_factory_.GetWeakPtr();
 }
diff --git a/content/browser/loader/resource_message_filter.h b/content/browser/loader/resource_message_filter.h
index 3b52a77..1240cb4 100644
--- a/content/browser/loader/resource_message_filter.h
+++ b/content/browser/loader/resource_message_filter.h
@@ -26,6 +26,8 @@ class URLRequestContext;
 namespace content {
 class ChromeAppCacheService;
 class ChromeBlobStorageContext;
+class HostZoomLevelContext;
+class HostZoomMap;
 class ResourceContext;
 class ServiceWorkerContextWrapper;
 
@@ -48,6 +50,7 @@ class CONTENT_EXPORT ResourceMessageFilter : public BrowserMessageFilter {
                         ChromeBlobStorageContext* blob_storage_context,
                         storage::FileSystemContext* file_system_context,
                         ServiceWorkerContextWrapper* service_worker_context,
+                        HostZoomLevelContext* host_zoom_level_context,
                         const GetContextsCallback& get_contexts_callback);
 
   // BrowserMessageFilter implementation.
@@ -77,6 +80,10 @@ class CONTENT_EXPORT ResourceMessageFilter : public BrowserMessageFilter {
     return service_worker_context_.get();
   }
 
+  // Returns a raw pointer to the HostZoomLevelContext's associated HostZoomMap,
+  // or NULL if no context is present.
+  const HostZoomMap* GetHostZoomMap() const;
+
   int child_id() const { return child_id_; }
   int process_type() const { return process_type_; }
 
@@ -96,6 +103,7 @@ class CONTENT_EXPORT ResourceMessageFilter : public BrowserMessageFilter {
   scoped_refptr<ChromeBlobStorageContext> blob_storage_context_;
   scoped_refptr<storage::FileSystemContext> file_system_context_;
   scoped_refptr<ServiceWorkerContextWrapper> service_worker_context_;
+  scoped_refptr<HostZoomLevelContext> host_zoom_level_context_;
 
   GetContextsCallback get_contexts_callback_;
 
diff --git a/content/browser/loader/resource_scheduler_unittest.cc b/content/browser/loader/resource_scheduler_unittest.cc
index 2d1b0fe..fb54951 100644
--- a/content/browser/loader/resource_scheduler_unittest.cc
+++ b/content/browser/loader/resource_scheduler_unittest.cc
@@ -120,6 +120,7 @@ class FakeResourceMessageFilter : public ResourceMessageFilter {
           NULL  /* blob_storage_context */,
           NULL  /* file_system_context */,
           NULL  /* service_worker_context */,
+          NULL  /* host_zoom_level_context */,
           base::Bind(&FakeResourceMessageFilter::GetContexts,
                      base::Unretained(this))) {
   }
diff --git a/content/browser/plugin_process_host.cc b/content/browser/plugin_process_host.cc
index dd969d3e..88b42ad 100644
--- a/content/browser/plugin_process_host.cc
+++ b/content/browser/plugin_process_host.cc
@@ -262,10 +262,11 @@ bool PluginProcessHost::Init(const WebPluginInfo& info) {
       base::Bind(&PluginProcessHost::GetContexts,
       base::Unretained(this)));
 
-  // TODO(jam): right now we're passing NULL for appcache, blob storage, and
-  // file system. If NPAPI plugins actually use this, we'll have to plumb them.
+  // TODO(jam): right now we're passing NULL for appcache, blob storage, file
+  // system and host zoom level context. If NPAPI plugins actually use this,
+  // we'll have to plumb them.
   ResourceMessageFilter* resource_message_filter = new ResourceMessageFilter(
-      process_->GetData().id, PROCESS_TYPE_PLUGIN, NULL, NULL, NULL, NULL,
+      process_->GetData().id, PROCESS_TYPE_PLUGIN, NULL, NULL, NULL, NULL, NULL,
       get_contexts_callback);
   process_->AddFilter(resource_message_filter);
   return true;
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index 84a31ba8..079f6e9dd 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -716,6 +716,7 @@ void RenderProcessHostImpl::CreateMessageFilters() {
       ChromeBlobStorageContext::GetFor(browser_context),
       storage_partition_impl_->GetFileSystemContext(),
       storage_partition_impl_->GetServiceWorkerContext(),
+      storage_partition_impl_->GetHostZoomLevelContext(),
       get_contexts_callback);
 
   AddFilter(resource_message_filter);
diff --git a/content/browser/renderer_host/render_view_host_impl.cc b/content/browser/renderer_host/render_view_host_impl.cc
index 8bafdab..e704fb6 100644
--- a/content/browser/renderer_host/render_view_host_impl.cc
+++ b/content/browser/renderer_host/render_view_host_impl.cc
@@ -1104,8 +1104,7 @@ void RenderViewHostImpl::OnDocumentAvailableInMainFrame(
     return;
 
   HostZoomMapImpl* host_zoom_map =
-      static_cast<HostZoomMapImpl*>(HostZoomMap::GetDefaultForBrowserContext(
-          GetProcess()->GetBrowserContext()));
+      static_cast<HostZoomMapImpl*>(HostZoomMap::Get(GetSiteInstance()));
   host_zoom_map->SetTemporaryZoomLevel(GetProcess()->GetID(),
                                        GetRoutingID(),
                                        host_zoom_map->GetDefaultZoomLevel());
@@ -1420,8 +1419,7 @@ void RenderViewHostImpl::NotifyMoveOrResizeStarted() {
 void RenderViewHostImpl::OnDidZoomURL(double zoom_level,
                                       const GURL& url) {
   HostZoomMapImpl* host_zoom_map =
-      static_cast<HostZoomMapImpl*>(HostZoomMap::GetDefaultForBrowserContext(
-          GetProcess()->GetBrowserContext()));
+      static_cast<HostZoomMapImpl*>(HostZoomMap::Get(GetSiteInstance()));
 
   host_zoom_map->SetZoomLevelForView(GetProcess()->GetID(),
                                      GetRoutingID(),
diff --git a/content/browser/resource_context_impl.cc b/content/browser/resource_context_impl.cc
index f9f3bc8..e7e4d0a 100644
--- a/content/browser/resource_context_impl.cc
+++ b/content/browser/resource_context_impl.cc
@@ -6,7 +6,6 @@
 
 #include "base/logging.h"
 #include "content/browser/fileapi/chrome_blob_storage_context.h"
-#include "content/browser/host_zoom_map_impl.h"
 #include "content/browser/loader/resource_dispatcher_host_impl.h"
 #include "content/browser/loader/resource_request_info_impl.h"
 #include "content/browser/streams/stream_context.h"
@@ -24,19 +23,9 @@ namespace {
 
 // Key names on ResourceContext.
 const char kBlobStorageContextKeyName[] = "content_blob_storage_context";
-const char kHostZoomMapKeyName[] = "content_host_zoom_map";
 const char kStreamContextKeyName[] = "content_stream_context";
 const char kURLDataManagerBackendKeyName[] = "url_data_manager_backend";
 
-class NonOwningZoomData : public base::SupportsUserData::Data {
- public:
-  explicit NonOwningZoomData(HostZoomMap* hzm) : host_zoom_map_(hzm) {}
-  HostZoomMap* host_zoom_map() { return host_zoom_map_; }
-
- private:
-  HostZoomMap* host_zoom_map_;
-};
-
 // Used by the default implementation of GetMediaDeviceIDSalt, below.
 std::string ReturnEmptySalt() {
   return std::string();
@@ -92,15 +81,6 @@ StreamContext* GetStreamContextForResourceContext(
       resource_context, kStreamContextKeyName);
 }
 
-HostZoomMap* GetHostZoomMapForResourceContext(ResourceContext* context) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
-  NonOwningZoomData* result = static_cast<NonOwningZoomData*>(
-      context->GetUserData(kHostZoomMapKeyName));
-  if (!result)
-    return NULL;
-  return result->host_zoom_map();
-}
-
 URLDataManagerBackend* GetURLDataManagerForResourceContext(
     ResourceContext* context) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
@@ -114,7 +94,6 @@ URLDataManagerBackend* GetURLDataManagerForResourceContext(
 
 void InitializeResourceContext(BrowserContext* browser_context) {
   ResourceContext* resource_context = browser_context->GetResourceContext();
-  DCHECK(!resource_context->GetUserData(kHostZoomMapKeyName));
 
   resource_context->SetUserData(
       kBlobStorageContextKeyName,
@@ -126,13 +105,6 @@ void InitializeResourceContext(BrowserContext* browser_context) {
       new UserDataAdapter<StreamContext>(
           StreamContext::GetFor(browser_context)));
 
-  // This object is owned by the BrowserContext and not ResourceContext, so
-  // store a non-owning pointer here.
-  resource_context->SetUserData(
-      kHostZoomMapKeyName,
-      new NonOwningZoomData(
-          HostZoomMap::GetDefaultForBrowserContext(browser_context)));
-
   resource_context->DetachUserDataThread();
 }
 
diff --git a/content/browser/resource_context_impl.h b/content/browser/resource_context_impl.h
index ed4de4d..d783484 100644
--- a/content/browser/resource_context_impl.h
+++ b/content/browser/resource_context_impl.h
@@ -12,7 +12,6 @@ namespace content {
 class ChromeBlobStorageContext;
 class StreamContext;
 class BrowserContext;
-class HostZoomMap;
 class URLDataManagerBackend;
 
 // Getters for objects that are part of BrowserContext which are also used on
@@ -25,8 +24,6 @@ ChromeBlobStorageContext* GetChromeBlobStorageContextForResourceContext(
 StreamContext* GetStreamContextForResourceContext(
     ResourceContext* resource_context);
 
-HostZoomMap* GetHostZoomMapForResourceContext(ResourceContext* context);
-
 URLDataManagerBackend* GetURLDataManagerForResourceContext(
     ResourceContext* context);
 
diff --git a/content/browser/storage_partition_impl.cc b/content/browser/storage_partition_impl.cc
index d4e49f6..d5b83bc 100644
--- a/content/browser/storage_partition_impl.cc
+++ b/content/browser/storage_partition_impl.cc
@@ -10,6 +10,7 @@
 #include "content/browser/fileapi/browser_file_system_helper.h"
 #include "content/browser/geofencing/geofencing_manager.h"
 #include "content/browser/gpu/shader_disk_cache.h"
+#include "content/browser/host_zoom_map_impl.h"
 #include "content/common/dom_storage/dom_storage_types.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/browser_thread.h"
@@ -368,7 +369,8 @@ StoragePartitionImpl::StoragePartitionImpl(
     ServiceWorkerContextWrapper* service_worker_context,
     WebRTCIdentityStore* webrtc_identity_store,
     storage::SpecialStoragePolicy* special_storage_policy,
-    GeofencingManager* geofencing_manager)
+    GeofencingManager* geofencing_manager,
+    HostZoomLevelContext* host_zoom_level_context)
     : partition_path_(partition_path),
       quota_manager_(quota_manager),
       appcache_service_(appcache_service),
@@ -379,7 +381,8 @@ StoragePartitionImpl::StoragePartitionImpl(
       service_worker_context_(service_worker_context),
       webrtc_identity_store_(webrtc_identity_store),
       special_storage_policy_(special_storage_policy),
-      geofencing_manager_(geofencing_manager) {
+      geofencing_manager_(geofencing_manager),
+      host_zoom_level_context_(host_zoom_level_context) {
 }
 
 StoragePartitionImpl::~StoragePartitionImpl() {
@@ -478,6 +481,10 @@ StoragePartitionImpl* StoragePartitionImpl::Create(
       new GeofencingManager(service_worker_context);
   geofencing_manager->Init();
 
+  scoped_refptr<HostZoomLevelContext> host_zoom_level_context(
+      new HostZoomLevelContext(
+          context->CreateZoomLevelDelegate(partition_path)));
+
   return new StoragePartitionImpl(partition_path,
                                   quota_manager.get(),
                                   appcache_service.get(),
@@ -488,7 +495,8 @@ StoragePartitionImpl* StoragePartitionImpl::Create(
                                   service_worker_context.get(),
                                   webrtc_identity_store.get(),
                                   special_storage_policy.get(),
-                                  geofencing_manager.get());
+                                  geofencing_manager.get(),
+                                  host_zoom_level_context.get());
 }
 
 base::FilePath StoragePartitionImpl::GetPath() {
@@ -536,6 +544,20 @@ GeofencingManager* StoragePartitionImpl::GetGeofencingManager() {
   return geofencing_manager_.get();
 }
 
+HostZoomMap* StoragePartitionImpl::GetHostZoomMap() {
+  DCHECK(host_zoom_level_context_.get());
+  return host_zoom_level_context_->GetHostZoomMap();
+}
+
+HostZoomLevelContext* StoragePartitionImpl::GetHostZoomLevelContext() {
+  return host_zoom_level_context_.get();
+}
+
+ZoomLevelDelegate* StoragePartitionImpl::GetZoomLevelDelegate() {
+  DCHECK(host_zoom_level_context_.get());
+  return host_zoom_level_context_->GetZoomLevelDelegate();
+}
+
 void StoragePartitionImpl::ClearDataImpl(
     uint32 remove_mask,
     uint32 quota_storage_remove_mask,
diff --git a/content/browser/storage_partition_impl.h b/content/browser/storage_partition_impl.h
index 3037739..bde83ad 100644
--- a/content/browser/storage_partition_impl.h
+++ b/content/browser/storage_partition_impl.h
@@ -10,6 +10,7 @@
 #include "base/memory/ref_counted.h"
 #include "content/browser/appcache/chrome_appcache_service.h"
 #include "content/browser/dom_storage/dom_storage_context_wrapper.h"
+#include "content/browser/host_zoom_level_context.h"
 #include "content/browser/indexed_db/indexed_db_context_impl.h"
 #include "content/browser/media/webrtc_identity_store.h"
 #include "content/browser/service_worker/service_worker_context_wrapper.h"
@@ -44,6 +45,9 @@ class StoragePartitionImpl : public StoragePartition {
   IndexedDBContextImpl* GetIndexedDBContext() override;
   ServiceWorkerContextWrapper* GetServiceWorkerContext() override;
   GeofencingManager* GetGeofencingManager() override;
+  HostZoomMap* GetHostZoomMap() override;
+  HostZoomLevelContext* GetHostZoomLevelContext() override;
+  ZoomLevelDelegate* GetZoomLevelDelegate() override;
 
   void ClearDataForOrigin(uint32 remove_mask,
                           uint32 quota_storage_remove_mask,
@@ -118,7 +122,8 @@ class StoragePartitionImpl : public StoragePartition {
       ServiceWorkerContextWrapper* service_worker_context,
       WebRTCIdentityStore* webrtc_identity_store,
       storage::SpecialStoragePolicy* special_storage_policy,
-      GeofencingManager* geofencing_manager);
+      GeofencingManager* geofencing_manager,
+      HostZoomLevelContext* host_zoom_level_context);
 
   void ClearDataImpl(uint32 remove_mask,
                      uint32 quota_storage_remove_mask,
@@ -159,6 +164,7 @@ class StoragePartitionImpl : public StoragePartition {
   scoped_refptr<WebRTCIdentityStore> webrtc_identity_store_;
   scoped_refptr<storage::SpecialStoragePolicy> special_storage_policy_;
   scoped_refptr<GeofencingManager> geofencing_manager_;
+  scoped_refptr<HostZoomLevelContext> host_zoom_level_context_;
 
   DISALLOW_COPY_AND_ASSIGN(StoragePartitionImpl);
 };
diff --git a/content/content_browser.gypi b/content/content_browser.gypi
index df70129..b43ec6e 100644
--- a/content/content_browser.gypi
+++ b/content/content_browser.gypi
@@ -239,6 +239,7 @@
       'public/browser/web_ui_message_handler.h',
       'public/browser/worker_service.h',
       'public/browser/worker_service_observer.h',
+      'public/browser/zoom_level_delegate.h',
       'public/browser/zygote_host_linux.h',
     ],
     'private_browser_sources': [
@@ -743,6 +744,8 @@
       'browser/histogram_subscriber.h',
       'browser/histogram_synchronizer.cc',
       'browser/histogram_synchronizer.h',
+      'browser/host_zoom_level_context.cc',
+      'browser/host_zoom_level_context.h',
       'browser/host_zoom_map_impl.cc',
       'browser/host_zoom_map_impl.h',
       'browser/indexed_db/indexed_db.h',
diff --git a/content/public/browser/browser_context.h b/content/public/browser/browser_context.h
index fec68dc..02b83e7 100644
--- a/content/public/browser/browser_context.h
+++ b/content/public/browser/browser_context.h
@@ -10,6 +10,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/supports_user_data.h"
 #include "content/common/content_export.h"
+#include "content/public/browser/zoom_level_delegate.h"
 #include "content/public/common/push_messaging_status.h"
 
 class GURL;
@@ -111,6 +112,11 @@ class CONTENT_EXPORT BrowserContext : public base::SupportsUserData {
 
   ~BrowserContext() override;
 
+  // Creates a delegate to initialize a HostZoomMap and persist its information.
+  // This is called during creation of each StoragePartition.
+  virtual scoped_ptr<ZoomLevelDelegate> CreateZoomLevelDelegate(
+      const base::FilePath& partition_path) = 0;
+
   // Returns the path of the directory where this context's data is stored.
   virtual base::FilePath GetPath() const = 0;
 
diff --git a/content/public/browser/host_zoom_map.h b/content/public/browser/host_zoom_map.h
index e9e523e..653d248 100644
--- a/content/public/browser/host_zoom_map.h
+++ b/content/public/browser/host_zoom_map.h
@@ -20,6 +20,7 @@ namespace content {
 class NavigationEntry;
 class BrowserContext;
 class ResourceContext;
+class SiteInstance;
 class WebContents;
 
 // Maps hostnames to custom zoom levels.  Written on the UI thread and read on
@@ -61,6 +62,17 @@ class HostZoomMap {
   CONTENT_EXPORT static HostZoomMap* GetDefaultForBrowserContext(
       BrowserContext* browser_context);
 
+  // Returns the HostZoomMap associated with this SiteInstance. The SiteInstance
+  // may serve multiple WebContents, and the HostZoomMap is the same for all of
+  // these WebContents.
+  CONTENT_EXPORT static HostZoomMap* Get(SiteInstance* instance);
+
+  // Returns the HostZoomMap associated with this WebContent's main frame. If
+  // multiple WebContents share the same SiteInstance, then they share a single
+  // HostZoomMap.
+  CONTENT_EXPORT static HostZoomMap* GetForWebContents(
+      const WebContents* contents);
+
   // Returns the current zoom level for the specified WebContents. May be
   // temporary or host-specific.
   CONTENT_EXPORT static double GetZoomLevel(const WebContents* web_contents);
diff --git a/content/public/browser/storage_partition.h b/content/public/browser/storage_partition.h
index c16e5e6..8335c05 100644
--- a/content/public/browser/storage_partition.h
+++ b/content/public/browser/storage_partition.h
@@ -40,10 +40,13 @@ namespace content {
 
 class AppCacheService;
 class BrowserContext;
+class HostZoomLevelContext;
+class HostZoomMap;
 class DOMStorageContext;
 class GeofencingManager;
 class IndexedDBContext;
 class ServiceWorkerContext;
+class ZoomLevelDelegate;
 
 // Defines what persistent state a child process can access.
 //
@@ -64,6 +67,9 @@ class CONTENT_EXPORT StoragePartition {
   virtual IndexedDBContext* GetIndexedDBContext() = 0;
   virtual ServiceWorkerContext* GetServiceWorkerContext() = 0;
   virtual GeofencingManager* GetGeofencingManager() = 0;
+  virtual HostZoomMap* GetHostZoomMap() = 0;
+  virtual HostZoomLevelContext* GetHostZoomLevelContext() = 0;
+  virtual ZoomLevelDelegate* GetZoomLevelDelegate() = 0;
 
   static const uint32 REMOVE_DATA_MASK_APPCACHE        = 1 << 0;
   static const uint32 REMOVE_DATA_MASK_COOKIES         = 1 << 1;
diff --git a/content/public/browser/zoom_level_delegate.h b/content/public/browser/zoom_level_delegate.h
new file mode 100644
index 0000000..e6a93bd
--- /dev/null
+++ b/content/public/browser/zoom_level_delegate.h
@@ -0,0 +1,21 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_PUBLIC_BROWSER_ZOOM_LEVEL_DELEGATE_H_
+#define CONTENT_PUBLIC_BROWSER_ZOOM_LEVEL_DELEGATE_H_
+
+namespace content {
+
+class HostZoomMap;
+
+// An interface to allow the client to initialize the HostZoomMap.
+class ZoomLevelDelegate {
+ public:
+  virtual void InitHostZoomMap(HostZoomMap* host_zoom_map) = 0;
+  virtual ~ZoomLevelDelegate() {}
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_ZOOM_LEVEL_DELEGATE_H_
diff --git a/content/public/test/mock_render_process_host.cc b/content/public/test/mock_render_process_host.cc
index 7b30a6f9..d98f6e8 100644
--- a/content/public/test/mock_render_process_host.cc
+++ b/content/public/test/mock_render_process_host.cc
@@ -13,6 +13,7 @@
 #include "content/browser/renderer_host/render_view_host_impl.h"
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/common/child_process_host_impl.h"
+#include "content/public/browser/browser_context.h"
 #include "content/public/browser/global_request_id.h"
 #include "content/public/browser/render_widget_host_iterator.h"
 #include "content/public/browser/storage_partition.h"
@@ -100,7 +101,7 @@ bool MockRenderProcessHost::IsIsolatedGuest() const {
 }
 
 StoragePartition* MockRenderProcessHost::GetStoragePartition() const {
-  return NULL;
+  return BrowserContext::GetDefaultStoragePartition(browser_context_);
 }
 
 void MockRenderProcessHost::AddWord(const base::string16& word) {
diff --git a/content/public/test/test_browser_context.cc b/content/public/test/test_browser_context.cc
index 2aab983..9c22851 100644
--- a/content/public/test/test_browser_context.cc
+++ b/content/public/test/test_browser_context.cc
@@ -59,6 +59,11 @@ base::FilePath TestBrowserContext::GetPath() const {
   return browser_context_dir_.path();
 }
 
+scoped_ptr<ZoomLevelDelegate> TestBrowserContext::CreateZoomLevelDelegate(
+    const base::FilePath& partition_path) {
+  return scoped_ptr<ZoomLevelDelegate>();
+}
+
 bool TestBrowserContext::IsOffTheRecord() const {
   return false;
 }
diff --git a/content/public/test/test_browser_context.h b/content/public/test/test_browser_context.h
index a736cb9..1310187 100644
--- a/content/public/test/test_browser_context.h
+++ b/content/public/test/test_browser_context.h
@@ -15,6 +15,7 @@
 
 namespace content {
 class MockResourceContext;
+class ZoomLevelDelegate;
 
 class TestBrowserContext : public BrowserContext {
  public:
@@ -28,6 +29,8 @@ class TestBrowserContext : public BrowserContext {
   void SetSpecialStoragePolicy(storage::SpecialStoragePolicy* policy);
 
   base::FilePath GetPath() const override;
+  scoped_ptr<ZoomLevelDelegate> CreateZoomLevelDelegate(
+      const base::FilePath& partition_path) override;
   bool IsOffTheRecord() const override;
   DownloadManagerDelegate* GetDownloadManagerDelegate() override;
   net::URLRequestContextGetter* GetRequestContext() override;
diff --git a/content/shell/browser/shell_browser_context.cc b/content/shell/browser/shell_browser_context.cc
index 8a97911..9f83562 100644
--- a/content/shell/browser/shell_browser_context.cc
+++ b/content/shell/browser/shell_browser_context.cc
@@ -95,6 +95,11 @@ void ShellBrowserContext::InitWhileIOAllowed() {
     base::CreateDirectory(path_);
 }
 
+scoped_ptr<ZoomLevelDelegate> ShellBrowserContext::CreateZoomLevelDelegate(
+    const base::FilePath&) {
+  return scoped_ptr<ZoomLevelDelegate>();
+}
+
 base::FilePath ShellBrowserContext::GetPath() const {
   return path_;
 }
diff --git a/content/shell/browser/shell_browser_context.h b/content/shell/browser/shell_browser_context.h
index d4e146f..2162ea0 100644
--- a/content/shell/browser/shell_browser_context.h
+++ b/content/shell/browser/shell_browser_context.h
@@ -23,6 +23,7 @@ namespace content {
 
 class DownloadManagerDelegate;
 class ShellDownloadManagerDelegate;
+class ZoomLevelDelegate;
 
 class ShellBrowserContext : public BrowserContext {
  public:
@@ -36,6 +37,8 @@ class ShellBrowserContext : public BrowserContext {
 
   // BrowserContext implementation.
   base::FilePath GetPath() const override;
+  scoped_ptr<ZoomLevelDelegate> CreateZoomLevelDelegate(
+      const base::FilePath& partition_path) override;
   bool IsOffTheRecord() const override;
   DownloadManagerDelegate* GetDownloadManagerDelegate() override;
   net::URLRequestContextGetter* GetRequestContext() override;