Prefetch @import files from CSS files.

Source/core/html/HTMLLinkElement.cpp

Index: Source/core/html/HTMLLinkElement.cpp
diff --git a/Source/core/html/HTMLLinkElement.cpp b/Source/core/html/HTMLLinkElement.cpp
index 5b1e253e9ae9ad5a0940b25817d3fca1bca46862..0f693fb47db4f5a224248607c0d769229cf0ef88 100644
--- a/Source/core/html/HTMLLinkElement.cpp
+++ b/Source/core/html/HTMLLinkElement.cpp
@@ -476,6 +476,8 @@ PassOwnPtrWillBeRawPtr<LinkStyle> LinkStyle::create(HTMLLinkElement* 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)
@@ -542,6 +544,29 @@ void LinkStyle::setCSSStyleSheet(const String& href, const KURL& baseURL, const
         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()) {