Prefetch @import files from CSS files.

Source/core/fetch/CSSStyleSheetResource.h

Index: Source/core/fetch/CSSStyleSheetResource.h
diff --git a/Source/core/fetch/CSSStyleSheetResource.h b/Source/core/fetch/CSSStyleSheetResource.h
index 35d0b0f9c63995d64785262535ace8e8215e646b..4bdc9a98e4ce543fa97d4b2da9306a50940499c5 100644
--- a/Source/core/fetch/CSSStyleSheetResource.h
+++ b/Source/core/fetch/CSSStyleSheetResource.h
@@ -28,6 +28,7 @@
 
 #include "core/fetch/ResourcePtr.h"
 #include "core/fetch/StyleSheetResource.h"
+#include "core/html/parser/CSSPreloadScanner.h"
 #include "heap/Handle.h"
 
 namespace WebCore {
@@ -39,7 +40,7 @@ class TextResourceDecoder;
 
 class CSSStyleSheetResource FINAL : public StyleSheetResource {
 public:
-    CSSStyleSheetResource(const ResourceRequest&, const String& charset);
+    CSSStyleSheetResource(const ResourceRequest&, const String& charset, Document*);

[abarth-chromium, 2014/02/26 19:13:36]

You can't have a dependency from a subclass of Resource to Document.  Resources
are shared by multiple documents.

     virtual ~CSSStyleSheetResource();
 
     const String sheetText(bool enforceMIMEType = true, bool* hasValidMIMEType = 0) const;
@@ -58,10 +59,15 @@ protected:
 private:
     bool canUseSheet(bool enforceMIMEType, bool* hasValidMIMEType) const;
     virtual void checkNotify() OVERRIDE;
+    virtual void appendData(const char*, int) OVERRIDE;
 
     OwnPtr<TextResourceDecoder> m_decoder;
     String m_decodedSheetText;
 
+    OwnPtr<CSSPreloadScanner> m_preloadScanner;
+    OwnPtr<HTMLResourcePreloader> m_preloader;
+    bool m_prescan;

[abarth-chromium, 2014/02/26 19:13:36]

What do m_prescan mean?  Does this mean m_isPreloadScanning?  Can we use the
nullity of m_preloadScanner to check for that instead?

+
     RefPtrWillBePersistent<StyleSheetContents> m_parsedStyleSheetCache;
 };