Add onChanged events to the extension settings API, both from sync and between

chrome/browser/extensions/extension_settings_api.h

Index: chrome/browser/extensions/extension_settings_api.h
diff --git a/chrome/browser/extensions/extension_settings_api.h b/chrome/browser/extensions/extension_settings_api.h
index 886319bb4f4c2737640cf270252b2a511ae516df..15f3fcb867bb10d89af4fd02e1de87bd2c5c50ca 100644
--- a/chrome/browser/extensions/extension_settings_api.h
+++ b/chrome/browser/extensions/extension_settings_api.h
@@ -21,11 +21,15 @@ class SettingsFunction : public AsyncExtensionFunction {
   //
   // Implementations should fill in args themselves, though (like RunImpl)
   // may return false to imply failure.
-  virtual bool RunWithStorage(ExtensionSettingsStorage* storage) = 0;
+  virtual bool RunWithStorage(
+      ExtensionSettingsBackend* backend,
+      ExtensionSettingsStorage* storage) = 0;
 
   // Sets error_ or result_ depending on the value of a storage Result, and
   // returns whether the Result implies success (i.e. !error).
-  bool UseResult(const ExtensionSettingsStorage::Result& storage_result);
+  bool UseResult(
+      ExtensionSettingsBackend* backend,
+      const ExtensionSettingsStorage::Result& storage_result);
 
  private:
   // Called via PostTask from RunImpl.  Calls RunWithStorage and then
@@ -38,7 +42,9 @@ class GetSettingsFunction : public SettingsFunction {
   DECLARE_EXTENSION_FUNCTION_NAME("experimental.settings.get");
 
  protected:
-  virtual bool RunWithStorage(ExtensionSettingsStorage* storage) OVERRIDE;
+  virtual bool RunWithStorage(
+      ExtensionSettingsBackend* backend,
+      ExtensionSettingsStorage* storage) OVERRIDE;
 };
 
 class SetSettingsFunction : public SettingsFunction {
@@ -46,7 +52,9 @@ class SetSettingsFunction : public SettingsFunction {
   DECLARE_EXTENSION_FUNCTION_NAME("experimental.settings.set");
 
  protected:
-  virtual bool RunWithStorage(ExtensionSettingsStorage* storage) OVERRIDE;
+  virtual bool RunWithStorage(
+      ExtensionSettingsBackend* backend,
+      ExtensionSettingsStorage* storage) OVERRIDE;
 };
 
 class RemoveSettingsFunction : public SettingsFunction {
@@ -54,7 +62,9 @@ class RemoveSettingsFunction : public SettingsFunction {
   DECLARE_EXTENSION_FUNCTION_NAME("experimental.settings.remove");
 
  protected:
-  virtual bool RunWithStorage(ExtensionSettingsStorage* storage) OVERRIDE;
+  virtual bool RunWithStorage(
+      ExtensionSettingsBackend* backend,
+      ExtensionSettingsStorage* storage) OVERRIDE;
 };
 
 class ClearSettingsFunction : public SettingsFunction {
@@ -62,7 +72,9 @@ class ClearSettingsFunction : public SettingsFunction {
   DECLARE_EXTENSION_FUNCTION_NAME("experimental.settings.clear");
 
  protected:
-  virtual bool RunWithStorage(ExtensionSettingsStorage* storage) OVERRIDE;
+  virtual bool RunWithStorage(
+      ExtensionSettingsBackend* backend,
+      ExtensionSettingsStorage* storage) OVERRIDE;
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_API_H_