Reland: Refactor code that defers extension background page loading

src/extensions depends on chrome::NOTIFICATION_PROFILE_CREATED to support
deferred loading of extension background pages when the profile isn't ready
yet. This is a layering violation.

* Remove Chrome concepts like "browser window ready" and "profile created"
from ProcessManager. Introduce ProcessManagerDelegate with a general concept
of deferring background page loading.
* Consolidate all the tricky Chrome-specific background page loading rules into
ChromeProcessManagerDelegate. This keeps all the rules in one place. Annotate
each block of special case code with the bug that inspired it.
* Extend unit test coverage for ProcessManager.

This will make it easier to eliminate chrome::NOTIFICATION_PROFILE_DESTROYED
in ProcessManager in a later CL.

(Original CL https://codereview.chromium.org/381283002 broke valgrind bots
because it was initializing left-over BrowserContextKeyedServices from tests
running earlier in the same process.)

BUG=392658
TEST=unit_tests ProcessManagerTest, browser_tests ProcessManagerBrowserTest, manual

Review URL: https://codereview.chromium.org/408523005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@284593 0039d316-1c4b-4281-b951-d872f2087c98

11 files changed, 291 insertions, 126 deletions

diff --git a/extensions/DEPS b/extensions/DEPS
index 0505b02..4077a55 100644
--- a/extensions/DEPS
+++ b/extensions/DEPS
@@ -1,4 +1,5 @@
 include_rules = [
+  # Do not add Chrome dependencies. Much work went into removing them.
   "+components/url_matcher",
   "+content/public/common",
   "+content/public/test",
@@ -13,7 +14,7 @@ include_rules = [
   # NOTE: Please do not add includes without talking to the app shell team;
   # see OWNERS for this directory.
   #
-  # TODO(jamescook): Remove these. http://crbug.com/162530
+  # TODO(jamescook): Remove this. http://crbug.com/392622
   "!chrome/browser/chrome_notification_types.h",
 ]
 
diff --git a/extensions/browser/extension_registry.h b/extensions/browser/extension_registry.h
index 75724cd..d11111c 100644
--- a/extensions/browser/extension_registry.h
+++ b/extensions/browser/extension_registry.h
@@ -43,6 +43,8 @@ class ExtensionRegistry : public KeyedService {
   // Returns the instance for the given |browser_context|.
   static ExtensionRegistry* Get(content::BrowserContext* browser_context);
 
+  content::BrowserContext* browser_context() const { return browser_context_; }
+
   // NOTE: These sets are *eventually* mututally exclusive, but an extension can
   // appear in two sets for short periods of time.
   const ExtensionSet& enabled_extensions() const {
diff --git a/extensions/browser/extensions_browser_client.h b/extensions/browser/extensions_browser_client.h
index 293b2af..cb810b6 100644
--- a/extensions/browser/extensions_browser_client.h
+++ b/extensions/browser/extensions_browser_client.h
@@ -41,6 +41,7 @@ class ExtensionPrefsObserver;
 class ExtensionSystem;
 class ExtensionSystemProvider;
 class InfoMap;
+class ProcessManagerDelegate;
 class RuntimeAPIDelegate;
 
 // Interface to allow the extensions module to make browser-process-specific
@@ -133,12 +134,9 @@ class ExtensionsBrowserClient {
       content::BrowserContext* context,
       std::vector<ExtensionPrefsObserver*>* observers) const = 0;
 
-  // Returns true if loading background pages should be deferred.
-  virtual bool DeferLoadingBackgroundHosts(
-      content::BrowserContext* context) const = 0;
-
-  virtual bool IsBackgroundPageAllowed(
-      content::BrowserContext* context) const = 0;
+  // Returns the ProcessManagerDelegate shared across all BrowserContexts. May
+  // return NULL in tests or for simple embedders.
+  virtual ProcessManagerDelegate* GetProcessManagerDelegate() const = 0;
 
   // Creates a new ExtensionHostDelegate instance.
   virtual scoped_ptr<ExtensionHostDelegate> CreateExtensionHostDelegate() = 0;
diff --git a/extensions/browser/lazy_background_task_queue_unittest.cc b/extensions/browser/lazy_background_task_queue_unittest.cc
index 0a991b4..bda663c 100644
--- a/extensions/browser/lazy_background_task_queue_unittest.cc
+++ b/extensions/browser/lazy_background_task_queue_unittest.cc
@@ -11,6 +11,7 @@
 #include "chrome/browser/extensions/test_extension_system.h"
 #include "chrome/test/base/testing_profile.h"
 #include "content/public/test/test_browser_thread_bundle.h"
+#include "extensions/browser/extension_registry.h"
 #include "extensions/browser/process_manager.h"
 #include "extensions/common/extension.h"
 #include "extensions/common/extension_builder.h"
@@ -22,7 +23,9 @@ namespace extensions {
 class TestProcessManager : public ProcessManager {
  public:
   explicit TestProcessManager(Profile* profile)
-      : ProcessManager(profile, profile->GetOriginalProfile()),
+      : ProcessManager(profile,
+                       profile->GetOriginalProfile(),
+                       ExtensionRegistry::Get(profile)),
         create_count_(0) {}
   virtual ~TestProcessManager() {}
 
diff --git a/extensions/browser/process_manager.cc b/extensions/browser/process_manager.cc
index e6beddb..72fbd2c 100644
--- a/extensions/browser/process_manager.cc
+++ b/extensions/browser/process_manager.cc
@@ -33,6 +33,7 @@
 #include "extensions/browser/extension_registry.h"
 #include "extensions/browser/extension_system.h"
 #include "extensions/browser/extensions_browser_client.h"
+#include "extensions/browser/process_manager_delegate.h"
 #include "extensions/browser/process_manager_observer.h"
 #include "extensions/browser/view_type_utils.h"
 #include "extensions/common/constants.h"
@@ -105,7 +106,8 @@ class IncognitoProcessManager : public ProcessManager {
  public:
   IncognitoProcessManager(BrowserContext* incognito_context,
                           BrowserContext* original_context,
-                          ProcessManager* original_manager);
+                          ProcessManager* original_manager,
+                          ExtensionRegistry* extension_registry);
   virtual ~IncognitoProcessManager() {}
   virtual bool CreateBackgroundHost(const Extension* extension,
                                     const GURL& url) OVERRIDE;
@@ -190,6 +192,7 @@ struct ProcessManager::BackgroundPageData {
 
 // static
 ProcessManager* ProcessManager::Create(BrowserContext* context) {
+  ExtensionRegistry* extension_registry = ExtensionRegistry::Get(context);
   ExtensionsBrowserClient* client = ExtensionsBrowserClient::Get();
   if (client->IsGuestSession(context)) {
     // In the guest session, there is a single off-the-record context.  Unlike
@@ -197,7 +200,7 @@ ProcessManager* ProcessManager::Create(BrowserContext* context) {
     // created regardless of whether extensions use "spanning" or "split"
     // incognito behavior.
     BrowserContext* original_context = client->GetOriginalContext(context);
-    return new ProcessManager(context, original_context);
+    return new ProcessManager(context, original_context, extension_registry);
   }
 
   if (context->IsOffTheRecord()) {
@@ -205,31 +208,46 @@ ProcessManager* ProcessManager::Create(BrowserContext* context) {
     ProcessManager* original_manager =
         ExtensionSystem::Get(original_context)->process_manager();
     return new IncognitoProcessManager(
-        context, original_context, original_manager);
+        context, original_context, original_manager, extension_registry);
   }
 
-  return new ProcessManager(context, context);
+  return new ProcessManager(context, context, extension_registry);
+}
+
+// static
+ProcessManager* ProcessManager::CreateForTesting(
+    BrowserContext* context,
+    ExtensionRegistry* extension_registry) {
+  DCHECK(!context->IsOffTheRecord());
+  return new ProcessManager(context, context, extension_registry);
 }
 
 // static
 ProcessManager* ProcessManager::CreateIncognitoForTesting(
     BrowserContext* incognito_context,
     BrowserContext* original_context,
-    ProcessManager* original_manager) {
+    ProcessManager* original_manager,
+    ExtensionRegistry* extension_registry) {
   DCHECK(incognito_context->IsOffTheRecord());
   DCHECK(!original_context->IsOffTheRecord());
-  return new IncognitoProcessManager(
-      incognito_context, original_context, original_manager);
+  return new IncognitoProcessManager(incognito_context,
+                                     original_context,
+                                     original_manager,
+                                     extension_registry);
 }
 
 ProcessManager::ProcessManager(BrowserContext* context,
-                               BrowserContext* original_context)
+                               BrowserContext* original_context,
+                               ExtensionRegistry* extension_registry)
     : site_instance_(SiteInstance::Create(context)),
+      extension_registry_(extension_registry),
       startup_background_hosts_created_(false),
       devtools_callback_(base::Bind(&ProcessManager::OnDevToolsStateChanged,
                                     base::Unretained(this))),
       last_background_close_sequence_id_(0),
       weak_ptr_factory_(this) {
+  // ExtensionRegistry is shared between incognito and regular contexts.
+  DCHECK_EQ(original_context, extension_registry_->browser_context());
   registrar_.Add(this, chrome::NOTIFICATION_EXTENSIONS_READY,
                  content::Source<BrowserContext>(original_context));
   registrar_.Add(this,
@@ -245,8 +263,6 @@ ProcessManager::ProcessManager(BrowserContext* context,
                  content::NotificationService::AllSources());
   registrar_.Add(this, content::NOTIFICATION_WEB_CONTENTS_CONNECTED,
                  content::NotificationService::AllSources());
-  registrar_.Add(this, chrome::NOTIFICATION_PROFILE_CREATED,
-                 content::Source<BrowserContext>(original_context));
   registrar_.Add(this, chrome::NOTIFICATION_PROFILE_DESTROYED,
                  content::Source<BrowserContext>(context));
   if (context->IsOffTheRecord()) {
@@ -307,11 +323,14 @@ bool ProcessManager::CreateBackgroundHost(const Extension* extension,
                                           const GURL& url) {
   // Hosted apps are taken care of from BackgroundContentsService. Ignore them
   // here.
-  if (extension->is_hosted_app() ||
-      !ExtensionsBrowserClient::Get()->
-          IsBackgroundPageAllowed(GetBrowserContext())) {
+  if (extension->is_hosted_app())
+    return false;
+
+  // Don't create hosts if the embedder doesn't allow it.
+  ProcessManagerDelegate* delegate =
+      ExtensionsBrowserClient::Get()->GetProcessManagerDelegate();
+  if (delegate && !delegate->IsBackgroundPageAllowed(GetBrowserContext()))
     return false;
-  }
 
   // Don't create multiple background hosts for an extension.
   if (GetBackgroundHostForExtension(extension->id()))
@@ -360,11 +379,7 @@ const Extension* ProcessManager::GetExtensionForRenderViewHost(
   if (!render_view_host->GetSiteInstance())
     return NULL;
 
-  ExtensionRegistry* registry = ExtensionRegistry::Get(GetBrowserContext());
-  if (!registry)
-    return NULL;
-
-  return registry->enabled_extensions().GetByID(
+  return extension_registry_->enabled_extensions().GetByID(
       GetExtensionID(render_view_host));
 }
 
@@ -440,9 +455,7 @@ void ProcessManager::DecrementLazyKeepaliveCount(
     const std::string& extension_id) {
   int& count = background_page_data_[extension_id].lazy_keepalive_count;
   DCHECK(count > 0 ||
-         !ExtensionRegistry::Get(GetBrowserContext())
-              ->enabled_extensions()
-              .Contains(extension_id));
+         !extension_registry_->enabled_extensions().Contains(extension_id));
 
   // If we reach a zero keepalive count when the lazy background page is about
   // to be closed, incrementing close_sequence_id will cancel the close
@@ -620,16 +633,6 @@ void ProcessManager::CancelSuspend(const Extension* extension) {
   }
 }
 
-void ProcessManager::OnBrowserWindowReady() {
-  // If the extension system isn't ready yet the background hosts will be
-  // created via NOTIFICATION_EXTENSIONS_READY below.
-  ExtensionSystem* system = ExtensionSystem::Get(GetBrowserContext());
-  if (!system->ready().is_signaled())
-    return;
-
-  CreateBackgroundHostsForProfileStartup();
-}
-
 content::BrowserContext* ProcessManager::GetBrowserContext() const {
   return site_instance_->GetBrowserContext();
 }
@@ -648,15 +651,10 @@ void ProcessManager::Observe(int type,
                              const content::NotificationSource& source,
                              const content::NotificationDetails& details) {
   switch (type) {
-    case chrome::NOTIFICATION_EXTENSIONS_READY:
-    case chrome::NOTIFICATION_PROFILE_CREATED: {
-       // Don't load background hosts now if the loading should be deferred.
-       // Instead they will be loaded when a browser window for this profile
-       // (or an incognito profile from this profile) is ready.
-       if (DeferLoadingBackgroundHosts())
-         break;
-
-      CreateBackgroundHostsForProfileStartup();
+    case chrome::NOTIFICATION_EXTENSIONS_READY: {
+      // TODO(jamescook): Convert this to use ExtensionSystem::ready() instead
+      // of a notification.
+      MaybeCreateStartupBackgroundHosts();
       break;
     }
 
@@ -784,24 +782,24 @@ void ProcessManager::OnDevToolsStateChanged(
   }
 }
 
-void ProcessManager::CreateBackgroundHostsForProfileStartup() {
-  if (startup_background_hosts_created_ ||
-      !ExtensionsBrowserClient::Get()->
-          IsBackgroundPageAllowed(GetBrowserContext())) {
+void ProcessManager::MaybeCreateStartupBackgroundHosts() {
+  if (startup_background_hosts_created_)
     return;
-  }
 
-  const ExtensionSet& enabled_extensions =
-      ExtensionRegistry::Get(GetBrowserContext())->enabled_extensions();
-  for (ExtensionSet::const_iterator extension = enabled_extensions.begin();
-       extension != enabled_extensions.end();
-       ++extension) {
-    CreateBackgroundHostForExtensionLoad(this, extension->get());
+  // The embedder might disallow background pages entirely.
+  ProcessManagerDelegate* delegate =
+      ExtensionsBrowserClient::Get()->GetProcessManagerDelegate();
+  if (delegate && !delegate->IsBackgroundPageAllowed(GetBrowserContext()))
+    return;
 
-    FOR_EACH_OBSERVER(ProcessManagerObserver,
-                      observer_list_,
-                      OnBackgroundHostStartup(*extension));
-  }
+  // The embedder might want to defer background page loading. For example,
+  // Chrome defers background page loading when it is launched to show the app
+  // list, then triggers a load later when a browser window opens.
+  if (delegate &&
+      delegate->DeferCreatingStartupBackgroundHosts(GetBrowserContext()))
+    return;
+
+  CreateStartupBackgroundHosts();
   startup_background_hosts_created_ = true;
 
   // Background pages should only be loaded once. To prevent any further loads
@@ -810,14 +808,6 @@ void ProcessManager::CreateBackgroundHostsForProfileStartup() {
       ExtensionsBrowserClient::Get()->GetOriginalContext(GetBrowserContext());
   if (registrar_.IsRegistered(
           this,
-          chrome::NOTIFICATION_PROFILE_CREATED,
-          content::Source<BrowserContext>(original_context))) {
-    registrar_.Remove(this,
-                      chrome::NOTIFICATION_PROFILE_CREATED,
-                      content::Source<BrowserContext>(original_context));
-  }
-  if (registrar_.IsRegistered(
-          this,
           chrome::NOTIFICATION_EXTENSIONS_READY,
           content::Source<BrowserContext>(original_context))) {
     registrar_.Remove(this,
@@ -826,6 +816,21 @@ void ProcessManager::CreateBackgroundHostsForProfileStartup() {
   }
 }
 
+void ProcessManager::CreateStartupBackgroundHosts() {
+  DCHECK(!startup_background_hosts_created_);
+  const ExtensionSet& enabled_extensions =
+      extension_registry_->enabled_extensions();
+  for (ExtensionSet::const_iterator extension = enabled_extensions.begin();
+       extension != enabled_extensions.end();
+       ++extension) {
+    CreateBackgroundHostForExtensionLoad(this, extension->get());
+
+    FOR_EACH_OBSERVER(ProcessManagerObserver,
+                      observer_list_,
+                      OnBackgroundHostStartup(*extension));
+  }
+}
+
 void ProcessManager::OnBackgroundHostCreated(ExtensionHost* host) {
   DCHECK_EQ(GetBrowserContext(), host->browser_context());
   background_hosts_.insert(host);
@@ -890,12 +895,6 @@ void ProcessManager::ClearBackgroundPageData(const std::string& extension_id) {
   }
 }
 
-bool ProcessManager::DeferLoadingBackgroundHosts() const {
-  // The extensions embedder may have special rules about background hosts.
-  return ExtensionsBrowserClient::Get()->DeferLoadingBackgroundHosts(
-      GetBrowserContext());
-}
-
 //
 // IncognitoProcessManager
 //
@@ -903,8 +902,9 @@ bool ProcessManager::DeferLoadingBackgroundHosts() const {
 IncognitoProcessManager::IncognitoProcessManager(
     BrowserContext* incognito_context,
     BrowserContext* original_context,
-    ProcessManager* original_manager)
-    : ProcessManager(incognito_context, original_context),
+    ProcessManager* original_manager,
+    ExtensionRegistry* extension_registry)
+    : ProcessManager(incognito_context, original_context, extension_registry),
       original_manager_(original_manager) {
   DCHECK(incognito_context->IsOffTheRecord());
 
@@ -914,8 +914,6 @@ IncognitoProcessManager::IncognitoProcessManager(
   // in the NOTIFICATION_BROWSER_WINDOW_READY notification handler.
   registrar_.Remove(this, chrome::NOTIFICATION_EXTENSIONS_READY,
                     content::Source<BrowserContext>(original_context));
-  registrar_.Remove(this, chrome::NOTIFICATION_PROFILE_CREATED,
-                    content::Source<BrowserContext>(original_context));
 }
 
 bool IncognitoProcessManager::CreateBackgroundHost(const Extension* extension,
@@ -932,14 +930,11 @@ bool IncognitoProcessManager::CreateBackgroundHost(const Extension* extension,
 }
 
 SiteInstance* IncognitoProcessManager::GetSiteInstanceForURL(const GURL& url) {
-  ExtensionRegistry* registry = ExtensionRegistry::Get(GetBrowserContext());
-  if (registry) {
-    const Extension* extension =
-        registry->enabled_extensions().GetExtensionOrAppByURL(url);
-    if (extension && !IncognitoInfo::IsSplitMode(extension)) {
-      return original_manager_->GetSiteInstanceForURL(url);
-    }
-  }
+  const Extension* extension =
+      extension_registry_->enabled_extensions().GetExtensionOrAppByURL(url);
+  if (extension && !IncognitoInfo::IsSplitMode(extension))
+    return original_manager_->GetSiteInstanceForURL(url);
+
   return ProcessManager::GetSiteInstanceForURL(url);
 }
 
diff --git a/extensions/browser/process_manager.h b/extensions/browser/process_manager.h
index e580bbd..e3c6bcf 100644
--- a/extensions/browser/process_manager.h
+++ b/extensions/browser/process_manager.h
@@ -33,6 +33,8 @@ namespace extensions {
 
 class Extension;
 class ExtensionHost;
+class ExtensionRegistry;
+class ProcessManagerDelegate;
 class ProcessManagerObserver;
 
 // Manages dynamic state of running Chromium extensions. There is one instance
@@ -122,8 +124,9 @@ class ProcessManager : public content::NotificationObserver {
   // onSuspendCanceled() event to it.
   void CancelSuspend(const Extension* extension);
 
-  // Ensures background hosts are loaded for a new browser window.
-  void OnBrowserWindowReady();
+  // Creates background hosts if the embedder is ready and they are not already
+  // loaded.
+  void MaybeCreateStartupBackgroundHosts();
 
   // Gets the BrowserContext associated with site_instance_ and all other
   // related SiteInstances.
@@ -137,18 +140,30 @@ class ProcessManager : public content::NotificationObserver {
   void SetKeepaliveImpulseDecrementCallbackForTesting(
       const ImpulseCallbackForTesting& callback);
 
-  // Creates an incognito-context instance for tests. Tests for non-incognito
-  // contexts can just use Create() above.
+  // Creates a non-incognito instance for tests. |registry| allows unit tests
+  // to inject an ExtensionRegistry that is not managed by the usual
+  // BrowserContextKeyedServiceFactory system.
+  static ProcessManager* CreateForTesting(content::BrowserContext* context,
+                                          ExtensionRegistry* registry);
+
+  // Creates an incognito-context instance for tests.
   static ProcessManager* CreateIncognitoForTesting(
       content::BrowserContext* incognito_context,
       content::BrowserContext* original_context,
-      ProcessManager* original_manager);
+      ProcessManager* original_manager,
+      ExtensionRegistry* registry);
+
+  bool startup_background_hosts_created_for_test() const {
+    return startup_background_hosts_created_;
+  }
 
  protected:
   // If |context| is incognito pass the master context as |original_context|.
-  // Otherwise pass the same context for both.
+  // Otherwise pass the same context for both. Pass the ExtensionRegistry for
+  // |context| as |registry|, or override it for testing.
   ProcessManager(content::BrowserContext* context,
-                 content::BrowserContext* original_context);
+                 content::BrowserContext* original_context,
+                 ExtensionRegistry* registry);
 
   // Called on browser shutdown to close our extension hosts.
   void CloseBackgroundHosts();
@@ -158,10 +173,6 @@ class ProcessManager : public content::NotificationObserver {
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
-  // Load all background pages once the profile data is ready and the pages
-  // should be loaded.
-  void CreateBackgroundHostsForProfileStartup();
-
   content::NotificationRegistrar registrar_;
 
   // The set of ExtensionHosts running viewless background extensions.
@@ -172,6 +183,9 @@ class ProcessManager : public content::NotificationObserver {
   // browsing instance is created.  This controls process grouping.
   scoped_refptr<content::SiteInstance> site_instance_;
 
+  // Not owned. Also used by IncognitoProcessManager.
+  ExtensionRegistry* extension_registry_;
+
  private:
   friend class ProcessManagerTest;
 
@@ -182,6 +196,10 @@ class ProcessManager : public content::NotificationObserver {
   typedef std::map<content::RenderViewHost*,
       extensions::ViewType> ExtensionRenderViews;
 
+  // Load all background pages once the profile data is ready and the pages
+  // should be loaded.
+  void CreateStartupBackgroundHosts();
+
   // Called just after |host| is created so it can be registered in our lists.
   void OnBackgroundHostCreated(ExtensionHost* host);
 
@@ -216,9 +234,6 @@ class ProcessManager : public content::NotificationObserver {
   // Clears background page data for this extension.
   void ClearBackgroundPageData(const std::string& extension_id);
 
-  // Returns true if loading background pages should be deferred.
-  bool DeferLoadingBackgroundHosts() const;
-
   void OnDevToolsStateChanged(content::DevToolsAgentHost*, bool attached);
 
   // Contains all active extension-related RenderViewHost instances for all
diff --git a/extensions/browser/process_manager_delegate.h b/extensions/browser/process_manager_delegate.h
new file mode 100644
index 0000000..7cc48c0
--- /dev/null
+++ b/extensions/browser/process_manager_delegate.h
@@ -0,0 +1,34 @@
+// 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 EXTENSIONS_BROWSER_PROCESS_MANAGER_DELEGATE_H_
+#define EXTENSIONS_BROWSER_PROCESS_MANAGER_DELEGATE_H_
+
+namespace content {
+class BrowserContext;
+};
+
+namespace extensions {
+
+// Customization of ProcessManager for the extension system embedder.
+class ProcessManagerDelegate {
+ public:
+  virtual ~ProcessManagerDelegate() {}
+
+  // Returns true if the embedder allows background pages for the given
+  // |context|.
+  virtual bool IsBackgroundPageAllowed(
+      content::BrowserContext* context) const = 0;
+
+  // Returns true if the embedder wishes to defer starting up the renderers for
+  // extension background pages. If the embedder returns true it must call
+  // ProcessManager::MaybeCreateStartupBackgroundHosts() when it is ready. See
+  // ChromeProcessManagerDelegate for examples of how this is useful.
+  virtual bool DeferCreatingStartupBackgroundHosts(
+      content::BrowserContext* context) const = 0;
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_PROCESS_MANAGER_DELEGATE_H_
diff --git a/extensions/browser/process_manager_unittest.cc b/extensions/browser/process_manager_unittest.cc
index b72b112..e5fc807 100644
--- a/extensions/browser/process_manager_unittest.cc
+++ b/extensions/browser/process_manager_unittest.cc
@@ -9,6 +9,8 @@
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/site_instance.h"
 #include "content/public/test/test_browser_context.h"
+#include "extensions/browser/extension_registry.h"
+#include "extensions/browser/process_manager_delegate.h"
 #include "extensions/browser/test_extensions_browser_client.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -33,12 +35,37 @@ class TestBrowserContextIncognito : public TestBrowserContext {
   DISALLOW_COPY_AND_ASSIGN(TestBrowserContextIncognito);
 };
 
+// A trivial ProcessManagerDelegate.
+class TestProcessManagerDelegate : public ProcessManagerDelegate {
+ public:
+  TestProcessManagerDelegate()
+      : is_background_page_allowed_(true),
+        defer_creating_startup_background_hosts_(false) {}
+  virtual ~TestProcessManagerDelegate() {}
+
+  // ProcessManagerDelegate implementation.
+  virtual bool IsBackgroundPageAllowed(BrowserContext* context) const OVERRIDE {
+    return is_background_page_allowed_;
+  }
+  virtual bool DeferCreatingStartupBackgroundHosts(
+      BrowserContext* context) const OVERRIDE {
+    return defer_creating_startup_background_hosts_;
+  }
+
+  bool is_background_page_allowed_;
+  bool defer_creating_startup_background_hosts_;
+};
+
 }  // namespace
 
 class ProcessManagerTest : public testing::Test {
  public:
-  ProcessManagerTest() : extensions_browser_client_(&original_context_) {
+  ProcessManagerTest()
+      : extension_registry_(&original_context_),
+        extensions_browser_client_(&original_context_) {
     extensions_browser_client_.SetIncognitoContext(&incognito_context_);
+    extensions_browser_client_.set_process_manager_delegate(
+        &process_manager_delegate_);
     ExtensionsBrowserClient::Set(&extensions_browser_client_);
   }
 
@@ -48,6 +75,10 @@ class ProcessManagerTest : public testing::Test {
 
   BrowserContext* original_context() { return &original_context_; }
   BrowserContext* incognito_context() { return &incognito_context_; }
+  ExtensionRegistry* extension_registry() { return &extension_registry_; }
+  TestProcessManagerDelegate* process_manager_delegate() {
+    return &process_manager_delegate_;
+  }
 
   // Returns true if the notification |type| is registered for |manager| with
   // source |context|. Pass NULL for |context| for all sources.
@@ -61,6 +92,8 @@ class ProcessManagerTest : public testing::Test {
  private:
   TestBrowserContext original_context_;
   TestBrowserContextIncognito incognito_context_;
+  ExtensionRegistry extension_registry_;  // Shared between BrowserContexts.
+  TestProcessManagerDelegate process_manager_delegate_;
   TestExtensionsBrowserClient extensions_browser_client_;
 
   DISALLOW_COPY_AND_ASSIGN(ProcessManagerTest);
@@ -69,8 +102,8 @@ class ProcessManagerTest : public testing::Test {
 // Test that notification registration works properly.
 TEST_F(ProcessManagerTest, ExtensionNotificationRegistration) {
   // Test for a normal context ProcessManager.
-  scoped_ptr<ProcessManager> manager1(
-      ProcessManager::Create(original_context()));
+  scoped_ptr<ProcessManager> manager1(ProcessManager::CreateForTesting(
+      original_context(), extension_registry()));
 
   EXPECT_EQ(original_context(), manager1->GetBrowserContext());
   EXPECT_EQ(0u, manager1->background_hosts().size());
@@ -90,8 +123,11 @@ TEST_F(ProcessManagerTest, ExtensionNotificationRegistration) {
                            original_context()));
 
   // Test for an incognito context ProcessManager.
-  scoped_ptr<ProcessManager> manager2(ProcessManager::CreateIncognitoForTesting(
-      incognito_context(), original_context(), manager1.get()));
+  scoped_ptr<ProcessManager> manager2(
+      ProcessManager::CreateIncognitoForTesting(incognito_context(),
+                                                original_context(),
+                                                manager1.get(),
+                                                extension_registry()));
 
   EXPECT_EQ(incognito_context(), manager2->GetBrowserContext());
   EXPECT_EQ(0u, manager2->background_hosts().size());
@@ -125,6 +161,83 @@ TEST_F(ProcessManagerTest, ExtensionNotificationRegistration) {
                            incognito_context()));
 }
 
+// Test that startup background hosts are created when the extension system
+// becomes ready.
+//
+// NOTE: This test and those that follow do not try to create ExtensionsHosts
+// because ExtensionHost is tightly coupled to WebContents and can't be
+// constructed in unit tests.
+TEST_F(ProcessManagerTest, CreateBackgroundHostsOnExtensionsReady) {
+  scoped_ptr<ProcessManager> manager(ProcessManager::CreateForTesting(
+      original_context(), extension_registry()));
+  ASSERT_FALSE(manager->startup_background_hosts_created_for_test());
+
+  // Simulate the extension system becoming ready.
+  content::NotificationService::current()->Notify(
+      chrome::NOTIFICATION_EXTENSIONS_READY,
+      content::Source<BrowserContext>(original_context()),
+      content::NotificationService::NoDetails());
+  EXPECT_TRUE(manager->startup_background_hosts_created_for_test());
+}
+
+// Test that startup background hosts can be created explicitly before the
+// extension system is ready (this is the normal pattern in Chrome).
+TEST_F(ProcessManagerTest, CreateBackgroundHostsExplicitly) {
+  scoped_ptr<ProcessManager> manager(ProcessManager::CreateForTesting(
+      original_context(), extension_registry()));
+  ASSERT_FALSE(manager->startup_background_hosts_created_for_test());
+
+  // Embedder explicitly asks for hosts to be created. Chrome does this on
+  // normal startup.
+  manager->MaybeCreateStartupBackgroundHosts();
+  EXPECT_TRUE(manager->startup_background_hosts_created_for_test());
+}
+
+// Test that the embedder can defer background host creation. Chrome does this
+// when the profile is created asynchronously, which may take a while.
+TEST_F(ProcessManagerTest, CreateBackgroundHostsDeferred) {
+  scoped_ptr<ProcessManager> manager(ProcessManager::CreateForTesting(
+      original_context(), extension_registry()));
+  ASSERT_FALSE(manager->startup_background_hosts_created_for_test());
+
+  // Don't create background hosts if the delegate says to defer them.
+  process_manager_delegate()->defer_creating_startup_background_hosts_ = true;
+  manager->MaybeCreateStartupBackgroundHosts();
+  EXPECT_FALSE(manager->startup_background_hosts_created_for_test());
+
+  // The extension system becoming ready still doesn't create the hosts.
+  content::NotificationService::current()->Notify(
+      chrome::NOTIFICATION_EXTENSIONS_READY,
+      content::Source<BrowserContext>(original_context()),
+      content::NotificationService::NoDetails());
+  EXPECT_FALSE(manager->startup_background_hosts_created_for_test());
+
+  // Once the embedder is ready the background hosts can be created.
+  process_manager_delegate()->defer_creating_startup_background_hosts_ = false;
+  manager->MaybeCreateStartupBackgroundHosts();
+  EXPECT_TRUE(manager->startup_background_hosts_created_for_test());
+}
+
+// Test that the embedder can disallow background host creation.
+// Chrome OS does this in guest mode.
+TEST_F(ProcessManagerTest, IsBackgroundHostAllowed) {
+  scoped_ptr<ProcessManager> manager(ProcessManager::CreateForTesting(
+      original_context(), extension_registry()));
+  ASSERT_FALSE(manager->startup_background_hosts_created_for_test());
+
+  // Don't create background hosts if the delegate disallows them.
+  process_manager_delegate()->is_background_page_allowed_ = false;
+  manager->MaybeCreateStartupBackgroundHosts();
+  EXPECT_FALSE(manager->startup_background_hosts_created_for_test());
+
+  // The extension system becoming ready still doesn't create the hosts.
+  content::NotificationService::current()->Notify(
+      chrome::NOTIFICATION_EXTENSIONS_READY,
+      content::Source<BrowserContext>(original_context()),
+      content::NotificationService::NoDetails());
+  EXPECT_FALSE(manager->startup_background_hosts_created_for_test());
+}
+
 // Test that extensions get grouped in the right SiteInstance (and therefore
 // process) based on their URLs.
 TEST_F(ProcessManagerTest, ProcessGrouping) {
@@ -133,12 +246,14 @@ TEST_F(ProcessManagerTest, ProcessGrouping) {
 
   // Extensions in different browser contexts should always be different
   // SiteInstances.
-  scoped_ptr<ProcessManager> manager1(
-      ProcessManager::Create(original_context()));
+  scoped_ptr<ProcessManager> manager1(ProcessManager::CreateForTesting(
+      original_context(), extension_registry()));
   // NOTE: This context is not associated with the TestExtensionsBrowserClient.
   // That's OK because we're not testing regular vs. incognito behavior.
   TestBrowserContext another_context;
-  scoped_ptr<ProcessManager> manager2(ProcessManager::Create(&another_context));
+  ExtensionRegistry another_registry(&another_context);
+  scoped_ptr<ProcessManager> manager2(
+      ProcessManager::CreateForTesting(&another_context, &another_registry));
 
   // Extensions with common origins ("scheme://id/") should be grouped in the
   // same SiteInstance.
diff --git a/extensions/browser/test_extensions_browser_client.cc b/extensions/browser/test_extensions_browser_client.cc
index dcd467f..a01b128 100644
--- a/extensions/browser/test_extensions_browser_client.cc
+++ b/extensions/browser/test_extensions_browser_client.cc
@@ -15,7 +15,9 @@ namespace extensions {
 
 TestExtensionsBrowserClient::TestExtensionsBrowserClient(
     BrowserContext* main_context)
-    : main_context_(main_context), incognito_context_(NULL) {
+    : main_context_(main_context),
+      incognito_context_(NULL),
+      process_manager_delegate_(NULL) {
   DCHECK(main_context_);
   DCHECK(!main_context_->IsOffTheRecord());
 }
@@ -116,14 +118,9 @@ void TestExtensionsBrowserClient::GetEarlyExtensionPrefsObservers(
     content::BrowserContext* context,
     std::vector<ExtensionPrefsObserver*>* observers) const {}
 
-bool TestExtensionsBrowserClient::DeferLoadingBackgroundHosts(
-    BrowserContext* context) const {
-  return false;
-}
-
-bool TestExtensionsBrowserClient::IsBackgroundPageAllowed(
-    BrowserContext* context) const {
-  return true;
+ProcessManagerDelegate* TestExtensionsBrowserClient::GetProcessManagerDelegate()
+    const {
+  return process_manager_delegate_;
 }
 
 scoped_ptr<ExtensionHostDelegate>
diff --git a/extensions/browser/test_extensions_browser_client.h b/extensions/browser/test_extensions_browser_client.h
index b793259..1cfffee 100644
--- a/extensions/browser/test_extensions_browser_client.h
+++ b/extensions/browser/test_extensions_browser_client.h
@@ -15,10 +15,14 @@ namespace extensions {
 // this class should call ExtensionsBrowserClient::Set() with its instance.
 class TestExtensionsBrowserClient : public ExtensionsBrowserClient {
  public:
-  // |context| is required and must not be an incognito context.
+  // |main_context| is required and must not be an incognito context.
   explicit TestExtensionsBrowserClient(content::BrowserContext* main_context);
   virtual ~TestExtensionsBrowserClient();
 
+  void set_process_manager_delegate(ProcessManagerDelegate* delegate) {
+    process_manager_delegate_ = delegate;
+  }
+
   // Associates an incognito context with |main_context_|.
   void SetIncognitoContext(content::BrowserContext* incognito_context);
 
@@ -59,10 +63,7 @@ class TestExtensionsBrowserClient : public ExtensionsBrowserClient {
   virtual void GetEarlyExtensionPrefsObservers(
       content::BrowserContext* context,
       std::vector<ExtensionPrefsObserver*>* observers) const OVERRIDE;
-  virtual bool DeferLoadingBackgroundHosts(
-      content::BrowserContext* context) const OVERRIDE;
-  virtual bool IsBackgroundPageAllowed(content::BrowserContext* context) const
-      OVERRIDE;
+  virtual ProcessManagerDelegate* GetProcessManagerDelegate() const OVERRIDE;
   virtual scoped_ptr<ExtensionHostDelegate> CreateExtensionHostDelegate()
       OVERRIDE;
   virtual bool DidVersionUpdate(content::BrowserContext* context) OVERRIDE;
@@ -82,6 +83,9 @@ class TestExtensionsBrowserClient : public ExtensionsBrowserClient {
   content::BrowserContext* main_context_;       // Not owned.
   content::BrowserContext* incognito_context_;  // Not owned, defaults to NULL.
 
+  // Not owned, defaults to NULL.
+  ProcessManagerDelegate* process_manager_delegate_;
+
   DISALLOW_COPY_AND_ASSIGN(TestExtensionsBrowserClient);
 };
 
diff --git a/extensions/extensions.gyp b/extensions/extensions.gyp
index 447dc32..35e8f38 100644
--- a/extensions/extensions.gyp
+++ b/extensions/extensions.gyp
@@ -433,6 +433,7 @@
         'browser/pref_names.h',
         'browser/process_manager.cc',
         'browser/process_manager.h',
+        'browser/process_manager_delegate.h',
         'browser/process_manager_observer.h',
         'browser/process_map.cc',
         'browser/process_map.h',