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

ui/base/resource/resource_bundle_ios.mm

Index: ui/base/resource/resource_bundle_ios.mm
diff --git a/ui/base/resource/resource_bundle_ios.mm b/ui/base/resource/resource_bundle_ios.mm
index 6ffb68754d951fbf4d553b23602034f41d42b930..a2e9295d9b02e95a2134e8570453b2b9f439b5e9 100644
--- a/ui/base/resource/resource_bundle_ios.mm
+++ b/ui/base/resource/resource_bundle_ios.mm
@@ -90,13 +90,12 @@ base::FilePath ResourceBundle::GetLocaleFilePath(const std::string& app_locale,
 }
 
 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;
@@ -166,7 +165,7 @@ gfx::Image& ResourceBundle::GetNativeImageNamed(int resource_id) {
     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))