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.
  * 2. Redistributions in binary form must reproduce the above copyright
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  *    documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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  */
 
 #include "core/html/parser/CSSPreloadScanner.h"
 
+#include "core/dom/Document.h"
+#include "core/fetch/CSSStyleSheetResource.h"
 #include "core/fetch/FetchInitiatorTypeNames.h"
+#include "core/frame/Settings.h"
 #include "core/html/parser/HTMLParserIdioms.h"
+#include "core/html/parser/HTMLResourcePreloader.h"
+#include "core/loader/DocumentLoader.h"
+#include "platform/Histogram.h"
 #include "platform/text/SegmentedString.h"
 #include <memory>
 
 namespace blink {
 
 CSSPreloadScanner::CSSPreloadScanner()
 {
 }
 
 CSSPreloadScanner::~CSSPreloadScanner()
@@ skipping 185 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_preloader(preloader)
+{
+    DCHECK(resource->getType() == Resource::Type::CSSStyleSheet);
+    setResource(toCSSStyleSheetResource(resource), Resource::DontMarkAsReferenced);
+}
+
+CSSPreloaderResourceClient::~CSSPreloaderResourceClient()
+{
+}
+
+void CSSPreloaderResourceClient::setCSSStyleSheet(const String& href, const KURL& baseURL, const String& charset, const CSSStyleSheetResource*)
+{
+    clearResource();
+}
+
+// Only attach for one appendData call, as that's where most imports will likely
+// be (according to spec).
+void CSSPreloaderResourceClient::didAppendFirstData(const CSSStyleSheetResource* resource)
+{
+    if (m_preloader)
+        scanCSS(resource);
+    clearResource();
+}
+
+void CSSPreloaderResourceClient::scanCSS(const CSSStyleSheetResource* resource)
+{
+    DCHECK(m_preloader);
+    CSSPreloadScanner cssPreloadScanner;
+    PreloadRequestStream preloads;
+    // Passing an empty SegmentedString here results in PreloadRequest with no
+    // file/line information.
+    // TODO(csharrison): If this becomes an issue the CSSPreloadScanner may be
+    // augmented to take care of this case without performing an additional
+    // copy.
+    const String& chunk = resource->decodedText();

[Charlie Harrison, 2016/08/26 04:16:37]

Let's add UMA here in a followup for the time it takes to perform this copy and
scan, so we know how much overhead this feature is adding.

+    if (!chunk.isNull()) {
+        cssPreloadScanner.scan(chunk, SegmentedString(), preloads, resource->response().url());
+    }
+    fetchPreloads(preloads);
+}
+
+void CSSPreloaderResourceClient::fetchPreloads(PreloadRequestStream& preloads)
+{
+    if (preloads.size()) {
+        m_preloader->document()->loader()->didObserveLoadingBehavior(WebLoadingBehaviorFlag::WebLoadingBehaviorCSSPreloadFound);
+    }
+
+    Settings* settings = m_preloader->document()->settings();
+    DCHECK(settings);
+    if (settings->cssExternalScannerPreload()) {
+        int currentPreloadCount = m_preloader->countPreloads();
+        m_preloader->takeAndPreload(preloads);
+        DEFINE_STATIC_LOCAL(CustomCountHistogram, cssImportHistogram, ("PreloadScanner.ExternalCSS.PreloadCount", 1, 100, 50));
+        cssImportHistogram.count(m_preloader->countPreloads() - currentPreloadCount);
+    }
+}
+
+DEFINE_TRACE(CSSPreloaderResourceClient)
+{
+    visitor->trace(m_preloader);
+    ResourceOwner<CSSStyleSheetResource>::trace(visitor);
+}
+
 } // namespace blink