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

ui/base/resource/resource_bundle_mac.mm

 // 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.
 
 #include "ui/base/resource/resource_bundle.h"
 
 #import <AppKit/AppKit.h>
 #include <stddef.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_);
-    if (images_.count(resource_id)) {
-      if (!images_[resource_id].HasRepresentation(gfx::Image::kImageRepCocoa)) {
-        DLOG(WARNING) << "ResourceBundle::GetNativeImageNamed() is returning a"
+  auto found = images_.find(resource_id);
+  if (found != images_.end()) {
+    if (!found->second.HasRepresentation(gfx::Image::kImageRepCocoa)) {
+      DLOG(WARNING)
+          << "ResourceBundle::GetNativeImageNamed() is returning a"
           << " cached gfx::Image that isn't backed by an NSImage. The image"
           << " will be converted, rather than going through the NSImage loader."
           << " resource_id = " << resource_id;
-      }
-      return images_[resource_id];
     }
+    return found->second;
   }
 
   gfx::Image image;
   if (delegate_)
     image = delegate_->GetNativeImageNamed(resource_id);
 
   if (image.IsEmpty()) {
     base::scoped_nsobject<NSImage> ns_image;
     for (size_t i = 0; i < data_packs_.size(); ++i) {
       scoped_refptr<base::RefCountedStaticMemory> data(
@@ skipping 38 matching lines @@
 
     if (!ns_image.get()) {
       LOG(WARNING) << "Unable to load image with id " << resource_id;
       NOTREACHED();  // Want to assert in debug mode.
       return GetEmptyImage();
     }
 
     image = gfx::Image(ns_image.release());
   }
 
-  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