Introduce ChromeZoomLevelPref, make zoom level prefs independent of profile prefs.

chrome/browser/ui/zoom/chrome_zoom_level_prefs.h

+// Copyright (c) 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 CHROME_BROWSER_UI_ZOOM_CHROME_ZOOM_LEVEL_PREFS_H_
+#define CHROME_BROWSER_UI_ZOOM_CHROME_ZOOM_LEVEL_PREFS_H_
+
+#include "base/callback.h"
+#include "base/files/file_path.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/observer_list.h"
+#include "base/prefs/json_pref_store.h"
+#include "base/prefs/pref_change_registrar.h"
+#include "base/prefs/pref_service.h"
+#include "base/prefs/pref_store.h"
+#include "content/public/browser/host_zoom_map.h"
+
+namespace chrome {
+
+// A class to implement the interface between the zoom levels (default and
+// per-host) and Chrome's preference persistence system.
+// Finally, the prefs are also updated in response to zoom events
+// from HostZoomMap.

[battre, 2014/10/06 14:33:51]

Can you work on the comment to better express what this class is in charge of?
Where authoritative data is stored and where it may be changed (i.e. what is the
flow of information)?

[wjmaclean, 2014/10/06 16:58:13]

Done.

+class ChromeZoomLevelPrefs {
+ public:
+  typedef base::CallbackList<void(void)>::Subscription
+      DefaultZoomLevelSubscription;
+
+  // Exposed as static function for testing.
+  static std::string GetHash(const base::FilePath& relative_path);
+
+  // Initialize the pref_service and the profile_path via the constructor,
+  // as these concepts won't be available in the content base class
+  // (to be added later) which will define the InitPrefsAndCopyToHostZoomMap
+  // interface. |pref_service_| must outlive this class.
+  ChromeZoomLevelPrefs(PrefService* pref_service,
+                       const base::FilePath& profile_path);
+  virtual ~ChromeZoomLevelPrefs();
+
+  virtual void InitPrefsAndCopyToHostZoomMap(
+      const base::FilePath& partition_path,
+      content::HostZoomMap* host_zoom_map);
+
+  void SetDefaultZoomLevelPref(double level);

[battre, 2014/10/06 14:33:51]

Currently both ChromeZoomLevelPrefs and HostZoomMap have setters. Can we have a
single API for this? I think it should be HostZoomMap.

[wjmaclean, 2014/10/06 16:58:13]

It is my understanding that the preferences are treated as a chrome content,
whereas HostZoomMap is purely a content/ construct. In content/ we use
HostZoomMap, but there needs to be a place in chrome to update the change in
preference. It is my intention that this will we that place, and all code in
chrome/ that wants to change default zoom level gors through here, and does not
talk directly to HostZoomMap.

+  double GetDefaultZoomLevelPref();

[battre, 2014/10/06 14:33:51]

const

[wjmaclean, 2014/10/06 16:58:13]

Done.

+  scoped_ptr<DefaultZoomLevelSubscription> RegisterDefaultZoomLevelCallback(
+      const base::Closure& callback);
+
+ private:
+  void OnZoomLevelChanged(const content::HostZoomMap::ZoomLevelChange& change);

[battre, 2014/10/06 14:33:51]

Please add a comment, who calls this and what it does.

[wjmaclean, 2014/10/06 16:58:13]

Done.

+
+  PrefService* pref_service_;
+  base::FilePath profile_path_;
+  content::HostZoomMap* host_zoom_map_;
+  scoped_ptr<content::HostZoomMap::Subscription> zoom_subscription_;
+  std::string partition_key_;
+  base::CallbackList<void(void)> default_zoom_changed_callbacks_;
+
+  DISALLOW_COPY_AND_ASSIGN(ChromeZoomLevelPrefs);
+};
+
+}  // namespace chrome
+
+#endif  // CHROME_BROWSER_UI_ZOOM_CHROME_ZOOM_LEVEL_PREFS_H_