Prefetch @import files from CSS files.

Source/core/fetch/CSSStyleSheetResource.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
@@ skipping 15 matching lines @@
 
 #include "config.h"
 #include "core/fetch/CSSStyleSheetResource.h"
 
 #include "core/css/StyleSheetContents.h"
 #include "core/fetch/ResourceClientWalker.h"
 #include "core/fetch/StyleSheetResourceClient.h"
 #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));
 
     // Prefer text/css but accept any type (dell.com serves a stylesheet
     // as text/html; see <http://bugs.webkit.org/show_bug.cgi?id=11451>).
     setAccept(acceptCSS);
 }
 
 CSSStyleSheetResource::~CSSStyleSheetResource()
 {
@@ skipping 63 matching lines @@
 {
     if (!isSafeToUnlock())
         return;
 
     m_parsedStyleSheetCache->removedFromMemoryCache();
     m_parsedStyleSheetCache.clear();
 
     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())
         return false;
 
     if (!enforceMIMEType && !hasValidMIMEType)
         return true;
 
     // This check exactly matches Firefox. Note that we grab the Content-Type
     // header directly because we want to see what the value is BEFORE content
@@ skipping 39 matching lines @@
 
     if (m_parsedStyleSheetCache)
         m_parsedStyleSheetCache->removedFromMemoryCache();
     m_parsedStyleSheetCache = sheet;
     m_parsedStyleSheetCache->addedToMemoryCache();
 
     setDecodedSize(m_parsedStyleSheetCache->estimatedSizeInBytes());
 }
 
 }