[Sync] Add favicon datatype proto support

sync/protocol/favicon_specifics.proto

+// 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.
+//
+// Sync protocol datatype extension for the favicons.
+
+syntax = "proto2";
+
+option optimize_for = LITE_RUNTIME;
+option retain_unknown_fields = true;
+
+package sync_pb;
+
+message FaviconData {
+  optional bytes favicon = 1;
+  // The favicon image's type. This should be kept in sync with IconType in
+  // history_types.cc

[pkotwicz, 2013/02/07 02:15:47]

Nit: history_types.h

+  enum IconType {
+    // A normal web favicon (max resolution 32x32).
+    FAVICON = 0;
+    // A high resolution touch favicon (max resolution 128x128)
+    TOUCH_ICON = 1;
+    // A precomposed touch favicon (max resolution xxx).

[pkotwicz, 2013/02/07 02:15:47]

It makes sense to cap the size of both TOUCH_ICON and TOUCH_PRECOMPOSED_ICON.
As far as I know, Chrome uses TOUCH_ICON and TOUCH_PRECOMPOSED_ICON icons
interchangeably.
Differentiating between the two is useful for validating the favicons from the
history service against the favicons that are provided by the site when a user
visits the site.

+    TOUCH_PRECOMPOSED_ICON = 2;
+  }
+  optional IconType icon_type = 2;
+  // The width in pixels of this favicon (which is assumed to be the same as
+  // the height).
+  optional int64 width = 3;

[pkotwicz, 2013/02/07 02:15:47]

We should sync both the width and height.

I think that we will want to sync the unresized favicon over sync.
If we do not, we will have to sync bitmap data resized to each of
16 * |screen_densities|
Where |screen_densities| is the set of all the supported screen densities by
Chromium. Android has way too many supported screen densities.

+}
+
+// Properties of Favicon objects.
+message FaviconSpecifics {
+  // The url of the favicon image.
+  optional string favicon_source = 1;

[pkotwicz, 2013/02/07 02:15:47]

Nit: Name this parameter |favicon_url| / |icon_url| / |url| ?

+  // The favicons associated with this source. Only one favicon per IconType
+  // is supported.
+  repeated FaviconData favicons = 2;
+  // The last time a page using this favicon was visited (in milliseconds
+  // since linux epoch). Once a favicon has not been visited in long enough
+  // time, it is garbage collected.
+  optional int64 last_visit_time_ms = 3;
+  // Whether this favicon is currently bookmarked or not. Bookmarked favicons
+  // are not garbage collected.
+  optional bool is_bookmarked = 4;
+}