Extension Storage API: expose storage quota information to extensions, via:

chrome/browser/extensions/settings/settings_quota_unittest.cc

 // 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 "testing/gtest/include/gtest/gtest.h"
 
 #include "base/json/json_writer.h"
 #include "base/values.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 31 matching lines @@
     ASSERT_EQ(256u, validate_sizes.size());
   }
 
   virtual void TearDown() OVERRIDE {
     ASSERT_TRUE(storage_.get() != NULL);
   }
 
  protected:
   // Creates |storage_|.  Must only be called once.
   void CreateStorage(
-      size_t quota_bytes, size_t quota_bytes_per_setting, size_t max_keys) {
+      size_t quota_bytes, size_t quota_bytes_per_item, size_t max_items) {
     ASSERT_TRUE(storage_.get() == NULL);
     SettingsStorageQuotaEnforcer::Limits limits =
-        { quota_bytes, quota_bytes_per_setting, max_keys };
+        { quota_bytes, quota_bytes_per_item, max_items };
     storage_.reset(new SettingsStorageQuotaEnforcer(limits, delegate_));
   }
 
   // Returns whether the settings in |storage_| and |delegate_| are the same as
   // |settings|.
   bool SettingsEqual(const DictionaryValue& settings) {
     return settings.Equals(&storage_->Get().settings()) &&
            settings.Equals(&delegate_->Get().settings());
   }
 
@@ skipping 484 matching lines @@
   EXPECT_FALSE(storage_->Set(IGNORE_QUOTA, "c", *byte_value_1_).HasError());
   EXPECT_FALSE(storage_->Set(IGNORE_QUOTA, "c", *byte_value_16_).HasError());
   settings.Set("c", byte_value_16_->DeepCopy());
 
   // ... except the last.  Make sure it can still fail.
   EXPECT_TRUE(storage_->Set(DEFAULTS, "c", *byte_value_256_).HasError());
 
   EXPECT_TRUE(SettingsEqual(settings));
 }
 
+TEST_F(ExtensionSettingsQuotaTest, GetBytesInUse) {
+  // Just testing GetBytesInUse, no need for a quota.
+  CreateStorage(UINT_MAX, UINT_MAX, UINT_MAX);
+
+  std::vector<std::string> ab;
+  ab.push_back("a");
+  ab.push_back("b");
+
+  EXPECT_EQ(0u, storage_->GetBytesInUse());
+  EXPECT_EQ(0u, storage_->GetBytesInUse("a"));
+  EXPECT_EQ(0u, storage_->GetBytesInUse("b"));
+  EXPECT_EQ(0u, storage_->GetBytesInUse(ab));
+
+  storage_->Set(DEFAULTS, "a", *byte_value_1_);
+
+  EXPECT_EQ(2u, storage_->GetBytesInUse());
+  EXPECT_EQ(2u, storage_->GetBytesInUse("a"));
+  EXPECT_EQ(0u, storage_->GetBytesInUse("b"));
+  EXPECT_EQ(2u, storage_->GetBytesInUse(ab));
+
+  storage_->Set(DEFAULTS, "b", *byte_value_1_);
+
+  EXPECT_EQ(4u, storage_->GetBytesInUse());
+  EXPECT_EQ(2u, storage_->GetBytesInUse("a"));
+  EXPECT_EQ(2u, storage_->GetBytesInUse("b"));
+  EXPECT_EQ(4u, storage_->GetBytesInUse(ab));
+
+  storage_->Set(DEFAULTS, "c", *byte_value_1_);
+
+  EXPECT_EQ(6u, storage_->GetBytesInUse());
+  EXPECT_EQ(2u, storage_->GetBytesInUse("a"));
+  EXPECT_EQ(2u, storage_->GetBytesInUse("b"));
+  EXPECT_EQ(4u, storage_->GetBytesInUse(ab));
+}
+
 }  // namespace extensions