Added preloader support for sizes based RW values

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 648 matching lines @@
 }
 
 void FrameFetchContext::addClientHintsIfNecessary(FetchRequest& fetchRequest)
 {
     if (!frame() || !RuntimeEnabledFeatures::clientHintsEnabled() || !m_document)
         return;
 
     if (frame()->shouldSendDPRHint())
         fetchRequest.mutableResourceRequest().addHTTPHeaderField("DPR", AtomicString(String::number(m_document->devicePixelRatio())));
 
-    // FIXME: Send the RW hint based on the actual resource width, when we have it.
-    if (frame()->shouldSendRWHint() && frame()->view())
-        fetchRequest.mutableResourceRequest().addHTTPHeaderField("RW", AtomicString(String::number(frame()->view()->viewportWidth())));
+    if (frame()->shouldSendRWHint() && frame()->view()) {
+        int resourceWidth = fetchRequest.resourceWidth();
+        if (resourceWidth < 0)

[Mike West, 2015/04/09 11:42:48]

Can resourceWidth reasonably be 0? It would be nice if we could make this
unsigned.

+            resourceWidth = frame()->view()->viewportWidth();
+        fetchRequest.mutableResourceRequest().addHTTPHeaderField("RW", AtomicString(String::number(resourceWidth)));
+    }
 }
 
 void FrameFetchContext::addCSPHeaderIfNecessary(Resource::Type type, FetchRequest& fetchRequest)
 {
     if (!document() || !frame())
         return;
 
     const ContentSecurityPolicy* csp = document()->contentSecurityPolicy();
     if (csp->shouldSendCSPHeader(type))
         fetchRequest.mutableResourceRequest().addHTTPHeaderField("CSP", "active");
 }
 
 DEFINE_TRACE(FrameFetchContext)
 {
     visitor->trace(m_document);
     FetchContext::trace(visitor);
 }
 
 } // namespace blink