Save large icons to a new LARGE_ICON type

components/favicon_base/favicon_types.h

Index: components/favicon_base/favicon_types.h
diff --git a/components/favicon_base/favicon_types.h b/components/favicon_base/favicon_types.h
index 469d0fa10b9890fee0cb5a83dc0aa2d71e8999a7..dfa7dbf00c9eba329ac2cad265d862606228ea4b 100644
--- a/components/favicon_base/favicon_types.h
+++ b/components/favicon_base/favicon_types.h
@@ -19,14 +19,30 @@ typedef int64 FaviconID;
 
 // Defines the icon types. They are also stored in icon_type field of favicons
 // table.
+//
 // The values of the IconTypes are used to select the priority in which favicon
 // data is returned in HistoryBackend and ThumbnailDatabase. Data for the
 // largest IconType takes priority if data for multiple IconTypes is available.
+//
+// Note: LARGE_ICON is a virtual icon type. In desktop environments, where
+//     favicons are small by default and larger touch icons are not the norm,

[huangs, 2015/05/04 20:00:44]

NIT: the indent's a bit unusual, but your call.

[Roger McFarlane (Chromium), 2015/05/04 20:16:56]

Done.

+//     it denotes the largest available icon the determined to be available. The
+//     underlying icon may have originated as a large FAVICON, a TOUCH_ICON, or
+//     a TOUCH_PRECOMPOSED_ICON. In mobile environments, larger sized icons are
+//     generally captured by default, so additional LARGE_ICON tagged icons are
+//     not stored. The LARGE_ICON type tag is only applied at the storage and
+//     query layers; icons are recognized using their true underlying type and,
+//     if it is determined that a large icon is desired but will not otherwise
+//     be captured, the backend selects the best candidate and saves it using
+//     the LARGE_ICON type. When querying for a large icon, all potential icon
+//     types are considered, and the returned results are evaluted based on
+//     the requested size.
 enum IconType {
   INVALID_ICON = 0x0,
   FAVICON = 1 << 0,
   TOUCH_ICON = 1 << 1,
-  TOUCH_PRECOMPOSED_ICON = 1 << 2
+  TOUCH_PRECOMPOSED_ICON = 1 << 2,
+  LARGE_ICON = 1 << 3
 };
 
 // Defines a gfx::Image of size desired_size_in_dip composed of image