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

chrome/browser/extensions/extension_settings_observer.h

+// Copyright (c) 2011 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 CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_OBSERVER_H_
+#define CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_OBSERVER_H_
+#pragma once
+
+#include "base/values.h"
+
+class Profile;
+
+// Interface for classes that listen to changes to extension settings.
+class ExtensionSettingsObserver {
+ public:
+  // A list of setting changes.  Use this class when building the event value,

[akalin, 2011/10/12 22:26:30]

i feel like this class should be in its own class -- since OnSettingsChanged
takes a string, it's not really related anymore.

[not at google - send to devlin, 2011/10/13 06:40:43]

Given comment below, still sensible to have this here?

[akalin, 2011/10/13 20:45:57]

I think so.  Less coupling is better.

[not at google - send to devlin, 2011/10/13 23:08:14]

Done.

+  // then pass the result of |GetEventJson| into |OnSettingsChanged|.
+  class ChangeList {
+   public:
+    ChangeList();
+    ~ChangeList();
+
+    // Appends a change for a setting.
+    void AppendChange(
+        const std::string& key,
+        // Ownership taken.  May be NULL to imply there is no old value.
+        Value* old_value,
+        // Ownership taken.  May be NULL to imply there is no new value.
+        Value* new_value);
+
+    // Gets the JSON serialization of the event.
+    std::string GetEventJson() const;
+
+   private:
+    ListValue changes_;
+  };
+
+  // Called when a list of settings have changed for an extension.
+  //
+  // |profile| is the profile of the event originator, or NULL if the event
+  // didn't originate from a background page.  This is so that events can avoid
+  // being sent back to the background page which made the change.  When the
+  // settings API is exposed to content scripts, this will need to be changed.
+  //
+  // |event_json| is the JSON serialization of the event to be passed directly
+  // to the onChanged listeners of the settings API.
+  virtual void OnSettingsChanged(
+      Profile* profile,
+      const std::string& extension_id,
+      const std::string& event_json) = 0;

[akalin, 2011/10/12 22:26:30]

I'm not really a fan of flattening into a string before passing it to observers.
 Would rather pass a const ChangeList& and let the observers flatten if
necessary.

This probably necessitates making ChangeList a wrapper around a ref-counted
inner class with the actual data

[not at google - send to devlin, 2011/10/13 06:40:43]

Done.

Though it's really very simple.  linked_ptr<ListValue> would be enough if it was
thread safe; the comments in linked_ptr mention shared_ptr but I can see no
evidence of this being available in Chromium.

[akalin, 2011/10/13 20:45:15]

shared_ptr isn't in Chromium and probably won't be, and linked_ptr isn't
thread-safe, so the only alternative is a RefCountedThreadSafe wrapper.

+
+ protected:
+  virtual ~ExtensionSettingsObserver();
+};
+
+#endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_SETTINGS_OBSERVER_H_