HTML Imports: Teach preloader about HTML Imports.

Source/core/html/parser/HTMLResourcePreloader.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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 55 matching lines @@
     }
     preconnect(host, crossOrigin);
 }
 
 void HTMLResourcePreloader::preload(PassOwnPtr<PreloadRequest> preload)
 {
     if (preload->isPreconnect()) {
         preconnectHost(preload.get());
         return;
     }
+    // TODO(yoichio): Should preload if document is imported.
     if (!m_document->loader())
         return;
     FetchRequest request = preload->resourceRequest(m_document);
-    if (preload->resourceType() == Resource::Script || preload->resourceType() == Resource::CSSStyleSheet)
+    if (preload->resourceType() == Resource::Script || preload->resourceType() == Resource::CSSStyleSheet || preload->resourceType() == Resource::ImportResource)
         request.setCharset(preload->charset().isEmpty() ? m_document->charset().string() : preload->charset());
     request.setForPreload(true);
     Platform::current()->histogramCustomCounts("WebCore.PreloadDelayMs", static_cast<int>(1000 * (monotonicallyIncreasingTime() - preload->discoveryTime())), 0, 2000, 20);
     m_document->loader()->startPreload(preload->resourceType(), request);
 }
 
 } // namespace blink