Prefetch @import files from CSS files.

Source/core/fetch/CSSStyleSheetResource.cpp

Index: Source/core/fetch/CSSStyleSheetResource.cpp
diff --git a/Source/core/fetch/CSSStyleSheetResource.cpp b/Source/core/fetch/CSSStyleSheetResource.cpp
index 1370b3bcb575081c6f1010f5c8ca43daac71b92b..62ca20f392603f71c859026240fc9a12bf009a50 100644
--- a/Source/core/fetch/CSSStyleSheetResource.cpp
+++ b/Source/core/fetch/CSSStyleSheetResource.cpp
@@ -33,14 +33,18 @@
 #include "core/html/parser/TextResourceDecoder.h"
 #include "platform/SharedBuffer.h"
 #include "platform/network/HTTPParsers.h"
+#include "platform/text/SegmentedString.h"
 #include "wtf/CurrentTime.h"
 #include "wtf/Vector.h"
 
 namespace WebCore {
 
-CSSStyleSheetResource::CSSStyleSheetResource(const ResourceRequest& resourceRequest, const String& charset)
+CSSStyleSheetResource::CSSStyleSheetResource(const ResourceRequest& resourceRequest, const String& charset, Document* document)
     : StyleSheetResource(resourceRequest, CSSStyleSheet)
     , m_decoder(TextResourceDecoder::create("text/css", charset))
+    , m_preloadScanner(adoptPtr(new CSSPreloadScanner))
+    , m_preloader(adoptPtr(new HTMLResourcePreloader(document)))

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

Why do we create these objects in the case where we're not going to use them? 
They're big complex objects.

+    , m_prescan(document ? true : false)

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

There's no reason to write foo ? true : false.  If the compiler can convert foo
to a Boolean for the ? : operator, then you can just store it directly.

 {
     DEFINE_STATIC_LOCAL(const AtomicString, acceptCSS, ("text/css,*/*;q=0.1", AtomicString::ConstructFromLiteral));
 
@@ -124,6 +128,17 @@ void CSSStyleSheetResource::destroyDecodedDataIfPossible()
     setDecodedSize(0);
 }
 
+void CSSStyleSheetResource::appendData(const char* data, int length)
+{
+    Resource::appendData(data, length);
+    if (m_prescan) {
+        m_prescan = false;
+        PreloadRequestStream pendingPreloads;
+        m_preloadScanner->scan(data, SegmentedString(data), pendingPreloads);
+        m_preloader->takeAndPreload(pendingPreloads);

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

Whey don't we destroy these objects when we're done with them?

+    }
+}
+
 bool CSSStyleSheetResource::canUseSheet(bool enforceMIMEType, bool* hasValidMIMEType) const
 {
     if (errorOccurred())