Make the low priority iframe flag affect all resources in cross origin iframes

Source/core/loader/FrameFetchContext.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 671 matching lines @@
 ResourceLoadPriority FrameFetchContext::modifyPriorityForExperiments(ResourceLoadPriority priority, Resource::Type type, const FetchRequest& request)
 {
     // An image fetch is used to distinguish between "early" and "late" scripts in a document
     if (type == Resource::Image)
         m_imageFetched = true;
 
     // If Settings is null, we can't verify any experiments are in force.
     if (!frame()->settings())
         return priority;
 
-    if (!frame()->isMainFrame() && frame()->settings()->lowPriorityIframes() && type == Resource::MainResource)
+    // If enabled, drop the priority of all resources in a subframe.
+    if (frame()->settings()->lowPriorityIframes() && !frame()->isMainFrame())
         return ResourceLoadPriorityVeryLow;
 
     // Async/Defer scripts.
     if (type == Resource::Script && FetchRequest::LazyLoad == request.defer())
         return frame()->settings()->fetchIncreaseAsyncScriptPriority() ? ResourceLoadPriorityMedium : ResourceLoadPriorityLow;
 
     // Runtime experiment that change how we prioritize resources.
     // The toggles do not depend on each other and can be flipped individually
     // though the cumulative result will depend on the interaction between them.
     // Background doc: https://docs.google.com/document/d/1bCDuq9H1ih9iNjgzyAL0gpwNFiEP4TZS-YLRp_RuMlc/edit?usp=sharing
@@ skipping 27 matching lines @@
 }
 
 DEFINE_TRACE(FrameFetchContext)
 {
     visitor->trace(m_document);
     visitor->trace(m_documentLoader);
     FetchContext::trace(visitor);
 }
 
 } // namespace blink