gfx::Image: Added thread checker.

chrome/browser/themes/browser_theme_pack.h

 // 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.
 
 #ifndef CHROME_BROWSER_THEMES_BROWSER_THEME_PACK_H_
 #define CHROME_BROWSER_THEMES_BROWSER_THEME_PACK_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 243 matching lines @@
   // non-NULL; |image_memory_| is only filled during BuildFromExtension(). Any
   // image data that needs to be written to the DataPack during WriteToDisk()
   // needs to be in |image_memory_|.
   RawImages image_memory_;
 
   // Loaded images. These are loaded from |image_memory_|, from |data_pack_|,
   // and by BuildFromExtension().
   ImageCache images_;
 
   // Cache of images created in BuildFromExtension(). Once the theme pack is
-  // created, this cache should only be accessed on the file thread. There
-  // should be no IDs in |image_memory_| that are in |images_on_file_thread_|
-  // or vice versa.
+  // created, this cache should only be accessed on the FILE thread (or whatever
+  // thread WriteToDisk is called from*). There should be no IDs in
+  // |image_memory_| that are in |images_on_file_thread_| or vice versa.
+  //
+  // *NOTE: These are usually accessed on the FILE thread, but as the
+  // documentation for WriteToDisk notes, it is not always the FILE thread; just
+  // some thread other than UI.
   ImageCache images_on_file_thread_;
 
   // Whether the theme pack has been succesfully initialized and is ready to
   // use.
   bool is_valid_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserThemePack);
 };
 
 #endif  // CHROME_BROWSER_THEMES_BROWSER_THEME_PACK_H_