Preload scan external css for @import

third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp

 /*
  * Copyright (C) 2008, 2010 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009 Torch Mobile, Inc. http://www.torchmobile.com/
  * Copyright (C) 2010 Google Inc. All Rights Reserved.
  *
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  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
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  *    documentation and/or other materials provided with the distribution.
  *
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  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 #include "core/html/parser/CSSPreloadScanner.h"
 
+#include "core/fetch/CSSStyleSheetResource.h"
 #include "core/fetch/FetchInitiatorTypeNames.h"
 #include "core/html/parser/HTMLParserIdioms.h"
+#include "core/html/parser/HTMLResourcePreloader.h"
+#include "platform/Histogram.h"
 #include "platform/text/SegmentedString.h"
 
 namespace blink {
 
 CSSPreloadScanner::CSSPreloadScanner()
 {
 }
 
 CSSPreloadScanner::~CSSPreloadScanner()
 {
@@ skipping 184 matching lines @@
         }
         m_state = Initial;
     } else if (equalIgnoringCase(m_rule, "charset"))
         m_state = Initial;
     else
         m_state = DoneParsingImportRules;
     m_rule.clear();
     m_ruleValue.clear();
 }
 
+CSSPreloaderResourceClient::CSSPreloaderResourceClient(Resource* resource, HTMLResourcePreloader* preloader)
+    : m_resource(resource)
+    , m_preloader(preloader)
+{
+}
+
+void CSSPreloaderResourceClient::notifyFinished(Resource* resource)
+{
+    resource->removeClient(this);
+}
+
+// Only attach for one appendData call, as that's where most imports will likely
+// be (according to spec).
+void CSSPreloaderResourceClient::didAppendFirstData(const CSSStyleSheetResource* resource)
+{
+    const String& chunk = resource->decodedText();
+    if (!chunk.isNull() && m_preloader) {
+        CSSPreloadScanner cssPreloadScanner;
+        PreloadRequestStream preloads;
+        // TODO(csharrison): Should SegmentedString be populated?

[kouhei (in TOK), 2016/04/25 22:10:05]

The only caveat of using empty SegmentedString here is that we will get
PreloadRequests without source file/line info. I'm not sure how important that
is.

[Charlie Harrison, 2016/04/25 22:29:12]

Yeah I know :/ I think leaving it out is okay, because @import should be the
first thing in the file besides charset. We could include it, but it would
entail a copy.

I'll leave it out for now and we can revisit if we decide to land this
experiment.

+        cssPreloadScanner.scan(chunk, SegmentedString(), preloads, resource->response().url());
+        int currentPreloadCount = m_preloader->countPreloads();
+        m_preloader->takeAndPreload(preloads);
+        DEFINE_STATIC_LOCAL(CustomCountHistogram, cssImportHistogram, ("CSSPreloaderResourceClient.PreloadCount", 1, 100, 50));
+        cssImportHistogram.count(m_preloader->countPreloads() - currentPreloadCount);
+    }
+    m_resource->removeClient(this);
+}
+
 } // namespace blink