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

content/public/browser/zoom_level_prefs_store.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 CONTENT_PUBLIC_BROWSER_ZOOM_LEVEL_PREFS_STORE_H_
+#define CONTENT_PUBLIC_BROWSER_ZOOM_LEVEL_PREFS_STORE_H_
+
+class PrefService;
+
+namespace base {
+class FilePath;
+}  // namespace base
+
+namespace content {
+
+class HostZoomMap;
+
+// An interface to manage a prefs store for (1) default zoom level, and

[Bernhard Bauer, 2014/09/12 10:28:49]

What exactly is a "prefs store" in this context? I'm asking because there is the
PrefStore class which is used by PrefService, but this isn't quite the same
thing, right?

[wjmaclean, 2014/09/16 18:44:44]

I guess the best way to describe this is to say that this is an interface for a
delegate that looks after initiallizing per-host zoom-level prefs (as was done
previously in profile), and also gives the embedder the option to persist them
(though content doesn't need to know about that part).

Is the name of the class problematic for content?

+// (2) per-host zoom levels. It can be used to load the latter into a
+// HostZoomMap.
+class ZoomLevelPrefsStore {
+ public:
+  virtual ~ZoomLevelPrefsStore() {}
+
+  virtual void InitPrefsAndCopyToHostZoomMap(const base::FilePath& file_path,
+                                             HostZoomMap* host_zoom_map) = 0;
+  virtual PrefService* GetPrefs() = 0;

[Bernhard Bauer, 2014/09/12 10:28:49]

This is a layering violation; content doesn't know about PrefService. Why does
this need to be in content anyway?

[wjmaclean, 2014/09/16 18:44:44]

Ok. I suppose I can remove this, and have clients in chrome convert to
ZoomLevelPrefsStoreImpl to get access.
I assume by "this" you mean this entire interface? Because when HostZoomMap
moves to StoragePartition, there needs to be a way to allow the embedder to
initialize (and possibly persist) zoom level values. Since the lifetime of the
HostZoomMap will managed by StoragePartition, it makes sense for the delegate to
live there also.

An overview of the full design is available at
https://docs.google.com/a/chromium.org/document/d/1SsWXDI0QGbRU1EQ6NQy8l1YLrZ...

+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_ZOOM_LEVEL_PREFS_STORE_H_