DomStorageCachedArea + DomStorageProxy interface and unittests. These classes aren't used yet.

BUG=94382
Review URL: https://chromiumcodereview.appspot.com/10450009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@138921 0039d316-1c4b-4281-b951-d872f2087c98

6 files changed, 680 insertions, 1 deletions

diff --git a/webkit/dom_storage/dom_storage_cached_area.cc b/webkit/dom_storage/dom_storage_cached_area.cc
new file mode 100644
index 0000000..6dfd1e5
--- /dev/null
+++ b/webkit/dom_storage/dom_storage_cached_area.cc
@@ -0,0 +1,194 @@
+// 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 "webkit/dom_storage/dom_storage_cached_area.h"
+
+#include "base/basictypes.h"
+#include "webkit/dom_storage/dom_storage_map.h"
+#include "webkit/dom_storage/dom_storage_proxy.h"
+
+namespace dom_storage {
+
+DomStorageCachedArea::DomStorageCachedArea(
+    int64 namespace_id, const GURL& origin, DomStorageProxy* proxy)
+    : ignore_all_mutations_(false),
+      namespace_id_(namespace_id), origin_(origin),
+      proxy_(proxy), weak_factory_(ALLOW_THIS_IN_INITIALIZER_LIST(this)) {
+}
+
+DomStorageCachedArea::~DomStorageCachedArea() {
+}
+
+unsigned DomStorageCachedArea::GetLength(int connection_id) {
+  PrimeIfNeeded(connection_id);
+  return map_->Length();
+}
+
+NullableString16 DomStorageCachedArea::GetKey(
+    int connection_id, unsigned index) {
+  PrimeIfNeeded(connection_id);
+  return map_->Key(index);
+}
+
+NullableString16 DomStorageCachedArea::GetItem(
+    int connection_id, const string16& key) {
+  PrimeIfNeeded(connection_id);
+  return map_->GetItem(key);
+}
+
+bool DomStorageCachedArea::SetItem(
+    int connection_id, const string16& key,
+    const string16& value, const GURL& page_url) {
+  // A quick check to reject obviously overbudget items to avoid
+  // the priming the cache.
+  if (key.length() + value.length() > dom_storage::kPerAreaQuota)
+    return false;
+
+  PrimeIfNeeded(connection_id);
+  NullableString16 unused;
+  if (!map_->SetItem(key, value, &unused))
+    return false;
+
+  // Ignore mutations to 'key' until OnSetItemComplete.
+  ignore_key_mutations_[key]++;
+  proxy_->SetItem(
+      connection_id, key, value, page_url,
+      base::Bind(&DomStorageCachedArea::OnSetItemComplete,
+                 weak_factory_.GetWeakPtr(), key));
+  return true;
+}
+
+void DomStorageCachedArea::RemoveItem(
+    int connection_id, const string16& key, const GURL& page_url) {
+  PrimeIfNeeded(connection_id);
+  string16 unused;
+  if (!map_->RemoveItem(key, &unused))
+    return;
+
+  // Ignore mutations to 'key' until OnRemoveItemComplete.
+  ignore_key_mutations_[key]++;
+  proxy_->RemoveItem(
+      connection_id, key, page_url,
+      base::Bind(&DomStorageCachedArea::OnRemoveItemComplete,
+                 weak_factory_.GetWeakPtr(), key));
+}
+
+void DomStorageCachedArea::Clear(int connection_id, const GURL& page_url) {
+  // No need to prime the cache in this case.
+  Reset();
+  map_ = new DomStorageMap(dom_storage::kPerAreaQuota);
+
+  // Ignore all mutations until OnClearComplete time.
+  ignore_all_mutations_ = true;
+  proxy_->ClearArea(
+      connection_id, page_url,
+      base::Bind(&DomStorageCachedArea::OnClearComplete,
+                 weak_factory_.GetWeakPtr()));
+}
+
+void DomStorageCachedArea::ApplyMutation(
+    const NullableString16& key, const NullableString16& new_value) {
+  if (!map_ || ignore_all_mutations_)
+    return;
+
+  if (key.is_null()) {
+    // It's a clear event.
+    scoped_refptr<DomStorageMap> old = map_;
+    map_ = new DomStorageMap(dom_storage::kPerAreaQuota);
+
+    // We have to retain local additions which happened after this
+    // clear operation from another process.
+    std::map<string16, int>::iterator iter = ignore_key_mutations_.begin();
+    while (iter != ignore_key_mutations_.end()) {
+      NullableString16 value = old->GetItem(iter->first);
+      if (!value.is_null()) {
+        NullableString16 unused;
+        map_->SetItem(iter->first, value.string(), &unused);
+      }
+      ++iter;
+    }
+    return;
+  }
+
+  // We have to retain local changes.
+  if (should_ignore_key_mutation(key.string()))
+    return;
+
+  if (new_value.is_null()) {
+    // It's a remove item event.
+    string16 unused;
+    map_->RemoveItem(key.string(), &unused);
+    return;
+  }
+
+  // It's a set item event.
+  // We turn off quota checking here to accomodate the over budget
+  // allowance that's provided in the browser process.
+  NullableString16 unused;
+  map_->set_quota(kint32max);
+  map_->SetItem(key.string(), new_value.string(), &unused);
+  map_->set_quota(dom_storage::kPerAreaQuota);
+}
+
+void DomStorageCachedArea::Prime(int connection_id) {
+  DCHECK(!map_);
+
+  // The LoadArea method is actually synchronous, but we have to
+  // wait for an asyncly delivered message to know when incoming
+  // mutation events should be applied. Our valuemap is plucked
+  // from ipc stream out of order, mutations in front if it need
+  // to be ignored.
+
+  // Ignore all mutations until OnLoadComplete time.
+  ignore_all_mutations_ = true;
+  ValuesMap values;
+  proxy_->LoadArea(
+      connection_id, &values,
+      base::Bind(&DomStorageCachedArea::OnLoadComplete,
+                 weak_factory_.GetWeakPtr()));
+  map_ = new DomStorageMap(dom_storage::kPerAreaQuota);
+  map_->SwapValues(&values);
+}
+
+void DomStorageCachedArea::Reset() {
+  map_ = NULL;
+  weak_factory_.InvalidateWeakPtrs();
+  ignore_key_mutations_.clear();
+  ignore_all_mutations_ = false;
+}
+
+void DomStorageCachedArea::OnLoadComplete(bool success) {
+  DCHECK(success);
+  DCHECK(ignore_all_mutations_);
+  ignore_all_mutations_ = false;
+}
+
+void DomStorageCachedArea::OnSetItemComplete(
+    const string16& key, bool success) {
+  if (!success) {
+    Reset();
+    return;
+  }
+  std::map<string16, int>::iterator found =  ignore_key_mutations_.find(key);
+  DCHECK(found != ignore_key_mutations_.end());
+  if (--found->second == 0)
+    ignore_key_mutations_.erase(found);
+}
+
+void DomStorageCachedArea::OnRemoveItemComplete(
+    const string16& key, bool success) {
+  DCHECK(success);
+  std::map<string16, int>::iterator found =  ignore_key_mutations_.find(key);
+  DCHECK(found != ignore_key_mutations_.end());
+  if (--found->second == 0)
+    ignore_key_mutations_.erase(found);
+}
+
+void DomStorageCachedArea::OnClearComplete(bool success) {
+  DCHECK(success);
+  DCHECK(ignore_all_mutations_);
+  ignore_all_mutations_ = false;
+}
+
+}  // namespace dom_storage
diff --git a/webkit/dom_storage/dom_storage_cached_area.h b/webkit/dom_storage/dom_storage_cached_area.h
new file mode 100644
index 0000000..1532afd
--- /dev/null
+++ b/webkit/dom_storage/dom_storage_cached_area.h
@@ -0,0 +1,87 @@
+// 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.
+
+#ifndef WEBKIT_DOM_STORAGE_DOM_STORAGE_CACHED_AREA_H_
+#define WEBKIT_DOM_STORAGE_DOM_STORAGE_CACHED_AREA_H_
+#pragma once
+
+#include <map>
+
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/nullable_string16.h"
+#include "googleurl/src/gurl.h"
+
+namespace dom_storage {
+
+class DomStorageMap;
+class DomStorageProxy;
+
+// Unlike the other classes in the dom_storage library, this one is intended
+// for use in renderer processes. It maintains a complete cach of the an
+// origin's Map of key/value pairs for fast access. The cache is primed on
+// first access and changes are written to the backend thru the |proxy|.
+// Mutations originating in other processes are applied to the cache via
+// the ApplyMutation method.
+class DomStorageCachedArea : public base::RefCounted<DomStorageCachedArea> {
+ public:
+  DomStorageCachedArea(int64 namespace_id, const GURL& origin,
+                       DomStorageProxy* proxy);
+
+  int64 namespace_id() const { return namespace_id_; }
+  const GURL& origin() const { return origin_; }
+
+  unsigned GetLength(int connection_id);
+  NullableString16 GetKey(int connection_id, unsigned index);
+  NullableString16 GetItem(int connection_id, const string16& key);
+  bool SetItem(int connection_id, const string16& key, const string16& value,
+               const GURL& page_url);
+  void RemoveItem(int connection_id, const string16& key,
+                  const GURL& page_url);
+  void Clear(int connection_id, const GURL& page_url);
+
+  void ApplyMutation(const NullableString16& key,
+                     const NullableString16& new_value);
+
+ private:
+  friend class DomStorageCachedAreaTest;
+  friend class base::RefCounted<DomStorageCachedArea>;
+  ~DomStorageCachedArea();
+
+  // Primes the cache, loading all values for the area.
+  void Prime(int connection_id);
+  void PrimeIfNeeded(int connection_id) {
+    if (!map_)
+      Prime(connection_id);
+  }
+
+  // Resets the object back to its newly constructed state.
+  void Reset();
+
+  // Async completion callbacks for proxied operations.
+  // These are used to maintain cache consistency by preventing
+  // mutation events from other processes from overwriting local
+  // changes made after the mutation.
+  void OnLoadComplete(bool success);
+  void OnSetItemComplete(const string16& key, bool success);
+  void OnClearComplete(bool success);
+  void OnRemoveItemComplete(const string16& key, bool success);
+
+  bool should_ignore_key_mutation(const string16& key) const {
+    return ignore_key_mutations_.find(key) != ignore_key_mutations_.end();
+  }
+
+  bool ignore_all_mutations_;
+  std::map<string16, int> ignore_key_mutations_;
+
+  int64 namespace_id_;
+  GURL origin_;
+  scoped_refptr<DomStorageMap> map_;
+  scoped_refptr<DomStorageProxy> proxy_;
+  base::WeakPtrFactory<DomStorageCachedArea> weak_factory_;
+};
+
+}  // namespace dom_storage
+
+#endif  // WEBKIT_DOM_STORAGE_DOM_STORAGE_CACHED_AREA_H_
diff --git a/webkit/dom_storage/dom_storage_cached_area_unittest.cc b/webkit/dom_storage/dom_storage_cached_area_unittest.cc
new file mode 100644
index 0000000..61b3cfe
--- /dev/null
+++ b/webkit/dom_storage/dom_storage_cached_area_unittest.cc
@@ -0,0 +1,349 @@
+// 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 <list>
+
+#include "base/bind.h"
+#include "base/utf_string_conversions.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "webkit/dom_storage/dom_storage_cached_area.h"
+#include "webkit/dom_storage/dom_storage_proxy.h"
+
+namespace dom_storage {
+
+namespace {
+// A mock implementation of the DomStorageProxy interface.
+class MockProxy : public DomStorageProxy {
+ public:
+  MockProxy() {
+    ResetObservations();
+  }
+
+  // DomStorageProxy interface for use by DomStorageCachedArea.
+
+  virtual void LoadArea(int connection_id, ValuesMap* values,
+                        const CompletionCallback& callback) OVERRIDE {
+    pending_callbacks_.push_back(callback);
+    observed_load_area_ = true;
+    observed_connection_id_ = connection_id;
+    *values = load_area_return_values_;
+  }
+
+  virtual void SetItem(int connection_id, const string16& key,
+                       const string16& value, const GURL& page_url,
+                       const CompletionCallback& callback) OVERRIDE {
+    pending_callbacks_.push_back(callback);
+    observed_set_item_ = true;
+    observed_connection_id_ = connection_id;
+    observed_key_ = key;
+    observed_value_ = value;
+    observed_page_url_ = page_url;
+  }
+
+  virtual void RemoveItem(int connection_id, const string16& key,
+                          const GURL& page_url,
+                          const CompletionCallback& callback) OVERRIDE {
+    pending_callbacks_.push_back(callback);
+    observed_remove_item_ = true;
+    observed_connection_id_ = connection_id;
+    observed_key_ = key;
+    observed_page_url_ = page_url;
+  }
+
+  virtual void ClearArea(int connection_id,
+                        const GURL& page_url,
+                        const CompletionCallback& callback) OVERRIDE {
+    pending_callbacks_.push_back(callback);
+    observed_clear_area_ = true;
+    observed_connection_id_ = connection_id;
+    observed_page_url_ = page_url;
+  }
+
+  // Methods and members for use by test fixtures.
+
+  void ResetObservations() {
+    observed_load_area_ = false;
+    observed_set_item_ = false;
+    observed_remove_item_ = false;
+    observed_clear_area_ = false;
+    observed_connection_id_ = 0;
+    observed_key_.clear();
+    observed_value_.clear();
+    observed_page_url_ = GURL();
+  }
+
+  void CompleteAllPendingCallbacks() {
+    while (!pending_callbacks_.empty())
+      CompleteOnePendingCallback(true);
+  }
+
+  void CompleteOnePendingCallback(bool success) {
+    ASSERT_TRUE(!pending_callbacks_.empty());
+    pending_callbacks_.front().Run(success);
+    pending_callbacks_.pop_front();
+  }
+
+  typedef std::list<CompletionCallback> CallbackList;
+
+  ValuesMap load_area_return_values_;
+  CallbackList pending_callbacks_;
+  bool observed_load_area_;
+  bool observed_set_item_;
+  bool observed_remove_item_;
+  bool observed_clear_area_;
+  int observed_connection_id_;
+  string16 observed_key_;
+  string16 observed_value_;
+  GURL observed_page_url_;
+
+ private:
+  virtual ~MockProxy() {}
+};
+}  // namespace
+
+class DomStorageCachedAreaTest : public testing::Test {
+ public:
+  DomStorageCachedAreaTest()
+    : kNamespaceId(10),
+      kOrigin("http://dom_storage/"),
+      kKey(ASCIIToUTF16("key")),
+      kValue(ASCIIToUTF16("value")),
+      kPageUrl("http://dom_storage/page") {
+  }
+
+  const int64 kNamespaceId;
+  const GURL kOrigin;
+  const string16 kKey;
+  const string16 kValue;
+  const GURL kPageUrl;
+
+  virtual void SetUp() {
+    mock_proxy_ = new MockProxy();
+  }
+
+  bool IsPrimed(DomStorageCachedArea* cached_area) {
+    return cached_area->map_.get();
+  }
+
+  bool IsIgnoringAllMutations(DomStorageCachedArea* cached_area) {
+    return cached_area->ignore_all_mutations_;
+  }
+
+  bool IsIgnoringKeyMutations(DomStorageCachedArea* cached_area,
+                              const string16& key) {
+    return cached_area->should_ignore_key_mutation(key);
+  }
+
+  void ResetAll(DomStorageCachedArea* cached_area) {
+    cached_area->Reset();
+    mock_proxy_->ResetObservations();
+    mock_proxy_->pending_callbacks_.clear();
+  }
+
+  void ResetCacheOnly(DomStorageCachedArea* cached_area) {
+    cached_area->Reset();
+  }
+
+ protected:
+  scoped_refptr<MockProxy> mock_proxy_;
+};
+
+TEST_F(DomStorageCachedAreaTest, Basics) {
+  EXPECT_TRUE(mock_proxy_->HasOneRef());
+  scoped_refptr<DomStorageCachedArea> cached_area =
+      new DomStorageCachedArea(kNamespaceId, kOrigin, mock_proxy_);
+  EXPECT_EQ(kNamespaceId, cached_area->namespace_id());
+  EXPECT_EQ(kOrigin, cached_area->origin());
+  EXPECT_FALSE(mock_proxy_->HasOneRef());
+  cached_area->ApplyMutation(NullableString16(kKey, false),
+                             NullableString16(kValue, false));
+  EXPECT_FALSE(IsPrimed(cached_area));
+
+  ResetAll(cached_area);
+  EXPECT_EQ(kNamespaceId, cached_area->namespace_id());
+  EXPECT_EQ(kOrigin, cached_area->origin());
+
+  const int kConnectionId = 1;
+  EXPECT_EQ(0u, cached_area->GetLength(kConnectionId));
+  EXPECT_TRUE(cached_area->SetItem(kConnectionId, kKey, kValue, kPageUrl));
+  EXPECT_EQ(1u, cached_area->GetLength(kConnectionId));
+  EXPECT_EQ(kKey, cached_area->GetKey(kConnectionId, 0).string());
+  EXPECT_EQ(kValue, cached_area->GetItem(kConnectionId, kKey).string());
+  cached_area->RemoveItem(kConnectionId, kKey, kPageUrl);
+  EXPECT_EQ(0u, cached_area->GetLength(kConnectionId));
+}
+
+TEST_F(DomStorageCachedAreaTest, Getters) {
+  const int kConnectionId = 7;
+  scoped_refptr<DomStorageCachedArea> cached_area =
+      new DomStorageCachedArea(kNamespaceId, kOrigin, mock_proxy_);
+
+  // GetLength, we expect to see one call to load in the proxy.
+  EXPECT_FALSE(IsPrimed(cached_area));
+  EXPECT_EQ(0u, cached_area->GetLength(kConnectionId));
+  EXPECT_TRUE(IsPrimed(cached_area));
+  EXPECT_TRUE(mock_proxy_->observed_load_area_);
+  EXPECT_EQ(kConnectionId, mock_proxy_->observed_connection_id_);
+  EXPECT_EQ(1u, mock_proxy_->pending_callbacks_.size());
+  EXPECT_TRUE(IsIgnoringAllMutations(cached_area));
+  mock_proxy_->CompleteAllPendingCallbacks();
+  EXPECT_FALSE(IsIgnoringAllMutations(cached_area));
+
+  // GetKey, expect the one call to load.
+  ResetAll(cached_area);
+  EXPECT_FALSE(IsPrimed(cached_area));
+  EXPECT_TRUE(cached_area->GetKey(kConnectionId, 2).is_null());
+  EXPECT_TRUE(IsPrimed(cached_area));
+  EXPECT_TRUE(mock_proxy_->observed_load_area_);
+  EXPECT_EQ(kConnectionId, mock_proxy_->observed_connection_id_);
+  EXPECT_EQ(1u, mock_proxy_->pending_callbacks_.size());
+
+  // GetItem, ditto.
+  ResetAll(cached_area);
+  EXPECT_FALSE(IsPrimed(cached_area));
+  EXPECT_TRUE(cached_area->GetItem(kConnectionId, kKey).is_null());
+  EXPECT_TRUE(IsPrimed(cached_area));
+  EXPECT_TRUE(mock_proxy_->observed_load_area_);
+  EXPECT_EQ(kConnectionId, mock_proxy_->observed_connection_id_);
+  EXPECT_EQ(1u, mock_proxy_->pending_callbacks_.size());
+}
+
+TEST_F(DomStorageCachedAreaTest, Setters) {
+  const int kConnectionId = 7;
+  scoped_refptr<DomStorageCachedArea> cached_area =
+      new DomStorageCachedArea(kNamespaceId, kOrigin, mock_proxy_);
+
+  // SetItem, we expect a call to load followed by a call to set item
+  // in the proxy.
+  EXPECT_FALSE(IsPrimed(cached_area));
+  EXPECT_TRUE(cached_area->SetItem(kConnectionId, kKey, kValue, kPageUrl));
+  EXPECT_TRUE(IsPrimed(cached_area));
+  EXPECT_TRUE(mock_proxy_->observed_load_area_);
+  EXPECT_TRUE(mock_proxy_->observed_set_item_);
+  EXPECT_EQ(kConnectionId, mock_proxy_->observed_connection_id_);
+  EXPECT_EQ(kPageUrl, mock_proxy_->observed_page_url_);
+  EXPECT_EQ(kKey, mock_proxy_->observed_key_);
+  EXPECT_EQ(kValue, mock_proxy_->observed_value_);
+  EXPECT_EQ(2u, mock_proxy_->pending_callbacks_.size());
+
+  // Clear, we expect a just the one call to clear in the proxy since
+  // there's no need to load the data prior to deleting it.
+  ResetAll(cached_area);
+  EXPECT_FALSE(IsPrimed(cached_area));
+  cached_area->Clear(kConnectionId, kPageUrl);
+  EXPECT_TRUE(IsPrimed(cached_area));
+  EXPECT_TRUE(mock_proxy_->observed_clear_area_);
+  EXPECT_EQ(kConnectionId, mock_proxy_->observed_connection_id_);
+  EXPECT_EQ(kPageUrl, mock_proxy_->observed_page_url_);
+  EXPECT_EQ(1u, mock_proxy_->pending_callbacks_.size());
+
+  // RemoveItem with nothing to remove, expect just one call to load.
+  ResetAll(cached_area);
+  EXPECT_FALSE(IsPrimed(cached_area));
+  cached_area->RemoveItem(kConnectionId, kKey, kPageUrl);
+  EXPECT_TRUE(IsPrimed(cached_area));
+  EXPECT_TRUE(mock_proxy_->observed_load_area_);
+  EXPECT_FALSE(mock_proxy_->observed_remove_item_);
+  EXPECT_EQ(kConnectionId, mock_proxy_->observed_connection_id_);
+  EXPECT_EQ(1u, mock_proxy_->pending_callbacks_.size());
+
+  // RemoveItem with something to remove, expect a call to load followed
+  // by a call to remove.
+  ResetAll(cached_area);
+  mock_proxy_->load_area_return_values_[kKey] = NullableString16(kValue, false);
+  EXPECT_FALSE(IsPrimed(cached_area));
+  cached_area->RemoveItem(kConnectionId, kKey, kPageUrl);
+  EXPECT_TRUE(IsPrimed(cached_area));
+  EXPECT_TRUE(mock_proxy_->observed_load_area_);
+  EXPECT_TRUE(mock_proxy_->observed_remove_item_);
+  EXPECT_EQ(kConnectionId, mock_proxy_->observed_connection_id_);
+  EXPECT_EQ(kPageUrl, mock_proxy_->observed_page_url_);
+  EXPECT_EQ(kKey, mock_proxy_->observed_key_);
+  EXPECT_EQ(2u, mock_proxy_->pending_callbacks_.size());
+}
+
+TEST_F(DomStorageCachedAreaTest, MutationsAreIgnoredUntilLoadCompletion) {
+  const int kConnectionId = 7;
+  scoped_refptr<DomStorageCachedArea> cached_area =
+      new DomStorageCachedArea(kNamespaceId, kOrigin, mock_proxy_);
+  EXPECT_TRUE(cached_area->GetItem(kConnectionId, kKey).is_null());
+  EXPECT_TRUE(IsPrimed(cached_area));
+  EXPECT_TRUE(IsIgnoringAllMutations(cached_area));
+
+  // Before load completion, the mutation should be ignored.
+  cached_area->ApplyMutation(NullableString16(kKey, false),
+                             NullableString16(kValue, false));
+  EXPECT_TRUE(cached_area->GetItem(kConnectionId, kKey).is_null());
+
+  // Call the load completion callback.
+  mock_proxy_->CompleteOnePendingCallback(true);
+  EXPECT_FALSE(IsIgnoringAllMutations(cached_area));
+
+  // Verify that mutations are now applied.
+  cached_area->ApplyMutation(NullableString16(kKey, false),
+                             NullableString16(kValue, false));
+  EXPECT_EQ(kValue, cached_area->GetItem(kConnectionId, kKey).string());
+}
+
+TEST_F(DomStorageCachedAreaTest, MutationsAreIgnoredUntilClearCompletion) {
+  const int kConnectionId = 4;
+  scoped_refptr<DomStorageCachedArea> cached_area =
+      new DomStorageCachedArea(kNamespaceId, kOrigin, mock_proxy_);
+  cached_area->Clear(kConnectionId, kPageUrl);
+  EXPECT_TRUE(IsIgnoringAllMutations(cached_area));
+  mock_proxy_->CompleteOnePendingCallback(true);
+  EXPECT_FALSE(IsIgnoringAllMutations(cached_area));
+
+  // Verify that calling Clear twice works as expected, the first
+  // completion callback should have been cancelled.
+  ResetCacheOnly(cached_area);
+  cached_area->Clear(kConnectionId, kPageUrl);
+  EXPECT_TRUE(IsIgnoringAllMutations(cached_area));
+  cached_area->Clear(kConnectionId, kPageUrl);
+  EXPECT_TRUE(IsIgnoringAllMutations(cached_area));
+  mock_proxy_->CompleteOnePendingCallback(true);
+  EXPECT_TRUE(IsIgnoringAllMutations(cached_area));
+  mock_proxy_->CompleteOnePendingCallback(true);
+  EXPECT_FALSE(IsIgnoringAllMutations(cached_area));
+}
+
+TEST_F(DomStorageCachedAreaTest, KeyMutationsAreIgnoredUntilCompletion) {
+  const int kConnectionId = 8;
+  scoped_refptr<DomStorageCachedArea> cached_area =
+      new DomStorageCachedArea(kNamespaceId, kOrigin, mock_proxy_);
+
+  // SetItem
+  EXPECT_TRUE(cached_area->SetItem(kConnectionId, kKey, kValue, kPageUrl));
+  mock_proxy_->CompleteOnePendingCallback(true);  // load completion
+  EXPECT_FALSE(IsIgnoringAllMutations(cached_area));
+  EXPECT_TRUE(IsIgnoringKeyMutations(cached_area, kKey));
+  cached_area->ApplyMutation(NullableString16(kKey, false),
+                             NullableString16(true));
+  EXPECT_EQ(kValue, cached_area->GetItem(kConnectionId, kKey).string());
+  mock_proxy_->CompleteOnePendingCallback(true);  // set completion
+  EXPECT_FALSE(IsIgnoringKeyMutations(cached_area, kKey));
+
+  // RemoveItem
+  cached_area->RemoveItem(kConnectionId, kKey, kPageUrl);
+  EXPECT_TRUE(IsIgnoringKeyMutations(cached_area, kKey));
+  mock_proxy_->CompleteOnePendingCallback(true);  // remove completion
+  EXPECT_FALSE(IsIgnoringKeyMutations(cached_area, kKey));
+
+  // Multiple mutations to the same key.
+  EXPECT_TRUE(cached_area->SetItem(kConnectionId, kKey, kValue, kPageUrl));
+  cached_area->RemoveItem(kConnectionId, kKey, kPageUrl);
+  EXPECT_TRUE(IsIgnoringKeyMutations(cached_area, kKey));
+  mock_proxy_->CompleteOnePendingCallback(true);  // set completion
+  EXPECT_TRUE(IsIgnoringKeyMutations(cached_area, kKey));
+  mock_proxy_->CompleteOnePendingCallback(true);  // remove completion
+  EXPECT_FALSE(IsIgnoringKeyMutations(cached_area, kKey));
+
+  // A failed set item operation should Reset the cache.
+  EXPECT_TRUE(cached_area->SetItem(kConnectionId, kKey, kValue, kPageUrl));
+  EXPECT_TRUE(IsIgnoringKeyMutations(cached_area, kKey));
+  mock_proxy_->CompleteOnePendingCallback(false);
+  EXPECT_FALSE(IsPrimed(cached_area));
+}
+
+}  // namespace dom_storage
diff --git a/webkit/dom_storage/dom_storage_map.h b/webkit/dom_storage/dom_storage_map.h
index 5a4b682..108716d 100644
--- a/webkit/dom_storage/dom_storage_map.h
+++ b/webkit/dom_storage/dom_storage_map.h
@@ -21,7 +21,7 @@ namespace dom_storage {
 class DomStorageMap
     : public base::RefCountedThreadSafe<DomStorageMap> {
  public:
-  DomStorageMap(size_t quota);
+  explicit DomStorageMap(size_t quota);
 
   unsigned Length() const;
   NullableString16 Key(unsigned index);
@@ -43,6 +43,8 @@ class DomStorageMap
   DomStorageMap* DeepCopy() const;
 
   size_t bytes_used() const { return bytes_used_; }
+  size_t quota() const { return quota_; }
+  void set_quota(size_t quota) { quota_ = quota; }
 
  private:
   friend class base::RefCountedThreadSafe<DomStorageMap>;
diff --git a/webkit/dom_storage/dom_storage_proxy.h b/webkit/dom_storage/dom_storage_proxy.h
new file mode 100644
index 0000000..81cae66
--- /dev/null
+++ b/webkit/dom_storage/dom_storage_proxy.h
@@ -0,0 +1,44 @@
+// 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.
+
+#ifndef WEBKIT_DOM_STORAGE_CACHED_AREA_H_
+#define WEBKIT_DOM_STORAGE_CACHED_AREA_H_
+#pragma once
+
+#include "base/bind.h"
+#include "base/memory/ref_counted.h"
+#include "base/nullable_string16.h"
+#include "base/string16.h"
+#include "googleurl/src/gurl.h"
+#include "webkit/dom_storage/dom_storage_types.h"
+
+namespace dom_storage {
+
+// Abstract interface for cached area, renderer to browser communications.
+class DomStorageProxy : public base::RefCounted<DomStorageProxy> {
+ public:
+  typedef base::Callback<void(bool)> CompletionCallback;
+
+  virtual void LoadArea(int connection_id, ValuesMap* values,
+                        const CompletionCallback& callback) = 0;
+
+  virtual void SetItem(int connection_id, const string16& key,
+                       const string16& value, const GURL& page_url,
+                       const CompletionCallback& callback) = 0;
+
+  virtual void RemoveItem(int connection_id, const string16& key,
+                          const GURL& page_url,
+                          const CompletionCallback& callback) = 0;
+
+  virtual void ClearArea(int connection_id,
+                         const GURL& page_url,
+                         const CompletionCallback& callback) = 0;
+ protected:
+  friend class base::RefCounted<DomStorageProxy>;
+  virtual ~DomStorageProxy() {}
+};
+
+}  // namespace dom_storage
+
+#endif  // WEBKIT_DOM_STORAGE_DOM_STORAGE_AREA_H_
diff --git a/webkit/dom_storage/webkit_dom_storage.gypi b/webkit/dom_storage/webkit_dom_storage.gypi
index 82f6670..525617d 100644
--- a/webkit/dom_storage/webkit_dom_storage.gypi
+++ b/webkit/dom_storage/webkit_dom_storage.gypi
@@ -18,6 +18,8 @@
       'sources': [
         'dom_storage_area.cc',
         'dom_storage_area.h',
+        'dom_storage_cached_area.cc',
+        'dom_storage_cached_area.h',
         'dom_storage_context.cc',
         'dom_storage_context.h',
         'dom_storage_database.cc',
@@ -28,6 +30,7 @@
         'dom_storage_map.h',
         'dom_storage_namespace.cc',
         'dom_storage_namespace.h',
+        'dom_storage_proxy.h',
         'dom_storage_session.cc',
         'dom_storage_session.h',
         'dom_storage_task_runner.cc',