Restrict cross-thread access to gfx::Image and gfx::Font in ResourceBundle

ui/base/resource/resource_bundle_ios.mm

 // Copyright 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.
 
 #include "ui/base/resource/resource_bundle.h"
 
 #import <QuartzCore/QuartzCore.h>
 #import <UIKit/UIKit.h>
 
 #include "base/files/file_path.h"
@@ skipping 72 matching lines @@
   if (locale_file_path.empty() || !locale_file_path.IsAbsolute())
     return base::FilePath();
 
   if (test_file_exists && !base::PathExists(locale_file_path))
     return base::FilePath();
 
   return locale_file_path;
 }
 
 gfx::Image& ResourceBundle::GetNativeImageNamed(int resource_id) {
+  DCHECK(sequence_checker_.CalledOnValidSequence());
+
   // Check to see if the image is already in the cache.
-  {
-    base::AutoLock lock(*images_and_fonts_lock_);
-    ImageMap::iterator found = images_.find(resource_id);
-    if (found != images_.end()) {
-      return found->second;
-    }
+  ImageMap::iterator found = images_.find(resource_id);
+  if (found != images_.end()) {
+    return found->second;
   }
 
   gfx::Image image;
   if (delegate_)
     image = delegate_->GetNativeImageNamed(resource_id);
 
   if (image.IsEmpty()) {
     // Load the raw data from the resource pack at the current supported scale
     // factor.  This code assumes that only one of the possible scale factors is
     // supported at runtime, based on the device resolution.
@@ skipping 49 matching lines @@
     if (!ui_image.get()) {
       LOG(WARNING) << "Unable to load image with id " << resource_id;
       NOTREACHED();  // Want to assert in debug mode.
       return GetEmptyImage();
     }
 
     // The gfx::Image takes ownership.
     image = gfx::Image(ui_image, base::scoped_policy::RETAIN);
   }
 
-  base::AutoLock lock(*images_and_fonts_lock_);
+  DCHECK(sequence_checker_.CalledOnValidSequence());
 
   // Another thread raced the load and has already cached the image.
   if (images_.count(resource_id))
     return images_[resource_id];
 
   images_[resource_id] = image;
   return images_[resource_id];
 }
 
 }  // namespace ui