Prefetch @import files from CSS files.

Source/core/html/HTMLLinkElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Rob Buis (rwlbuis@gmail.com)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 458 matching lines @@
     HTMLElement::attributeWillChange(name, oldValue, newValue);
 }
 
 PassOwnPtrWillBeRawPtr<LinkStyle> LinkStyle::create(HTMLLinkElement* owner)
 {
     return adoptPtrWillBeNoop(new LinkStyle(owner));
 }
 
 LinkStyle::LinkStyle(HTMLLinkElement* owner)
     : LinkResource(owner)
+    , m_preloadScanner(adoptPtr(new CSSPreloadScanner))
+    , m_preloadInput(adoptPtr(new SegmentedString))
     , m_disabledState(Unset)
     , m_pendingSheetType(None)
     , m_loading(false)
     , m_firedLoad(false)
     , m_loadedSheet(false)
 {
 }
 
 LinkStyle::~LinkStyle()
 {
@@ skipping 46 matching lines @@
     styleSheet->parseAuthorStyleSheet(cachedStyleSheet, m_owner->document().securityOrigin());
 
     m_loading = false;
     styleSheet->notifyLoadedSheet(cachedStyleSheet);
     styleSheet->checkLoaded();
 
     if (styleSheet->isCacheable())
         const_cast<CSSStyleSheetResource*>(cachedStyleSheet)->saveParsedStyleSheet(styleSheet);
 }
 
+void LinkStyle::dataReceived(const CSSStyleSheetResource* cachedStyleSheet, const char* data, int length)
+{
+    if (!m_preloadScanner)
+        return;
+
+    PreloadRequestStream pendingPreloads;
+    m_preloadInput->append(SegmentedString(String(data, length)));

[abarth-chromium, 2014/07/29 16:43:52]

How can you take a const char* and make a String out of it?  What encoding is
|data| in?  Don't we need to run it through the appropriate decoder?

+    m_preloadScanner->scan(data, *m_preloadInput, pendingPreloads);
+
+    OwnPtr<HTMLResourcePreloader> preloader = HTMLResourcePreloader::create(document());
+    preloader->takeAndPreload(pendingPreloads);
+    if (m_preloadScanner->isDoneParsingImports()) {
+        // Note: Although dataRecieved will be called for each packet of data
+        // returned from the network, @import statements are always at the top
+        // of the CSS file. As soon as we reach a part of the CSS file which
+        // is not an @import we can delete our preloader and ignore the rest of
+        // file. If we ever make CSS preloading more complicated (to look for
+        // URLs other than @imports) we will need to re-think this logic.
+        m_preloadScanner.clear();
+        m_preloadInput.clear();
+    }
+}
+
 bool LinkStyle::sheetLoaded()
 {
     if (!styleSheetIsLoading()) {
         removePendingSheet();
         return true;
     }
     return false;
 }
 
 void LinkStyle::notifyLoadedSheetAndAllCriticalSubresources(bool errorOccurred)
@@ skipping 186 matching lines @@
         removePendingSheet();
 }
 
 void LinkStyle::trace(Visitor* visitor)
 {
     visitor->trace(m_sheet);
     LinkResource::trace(visitor);
 }
 
 } // namespace blink