Preload scan external CSS for @import

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

Index: third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp
diff --git a/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp b/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp
index 939aa3836a892d4162a09e8d86ce1e8046e7d0b7..b8142f0a950c92f6b800ef1036b0b3490a74af12 100644
--- a/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp
+++ b/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp
@@ -27,8 +27,14 @@
 
 #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"
 
 namespace blink {
@@ -233,4 +239,71 @@ void CSSPreloadScanner::emitRule(const SegmentedString& source)
     m_ruleValue.clear();
 }
 
+CSSPreloaderResourceClient::CSSPreloaderResourceClient(Resource* resource, HTMLResourcePreloader* preloader)
+    : m_resource(resource)
+    , m_preloader(preloader)
+{
+}
+
+CSSPreloaderResourceClient::~CSSPreloaderResourceClient()

[hiroshige, 2016/06/17 12:15:17]

We don't need this destructor if we make CSSPreloaderResourceClient to be a
ResourceOwner. (clearResource() is called by ResourceOwner's prefinalizer)

[Charlie Harrison, 2016/07/13 18:18:14]

Done.

+{
+    clearResource();
+}
+
+void CSSPreloaderResourceClient::notifyFinished(Resource* resource)
+{
+    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::clearResource()

[hiroshige, 2016/06/17 12:15:17]

We can remove this if we make CSSPreloaderResourceClient to be a ResourceOwner.

[Charlie Harrison, 2016/07/13 18:18:14]

Done.

+{
+    if (m_resource) {
+        m_resource->removeClient(this);
+        m_resource.clear();
+    }
+}
+
+void CSSPreloaderResourceClient::scanCSS(const CSSStyleSheetResource* resource)
+{
+    DCHECK(m_preloader);
+    Settings* settings = m_preloader->document()->settings();
+    if (!settings)
+        return;
+    if (!settings->cssExternalScannerNoPreload() && !settings->cssExternalScannerPreload()) {
+        return;
+    }
+
+    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();
+    if (!chunk.isNull()) {
+        cssPreloadScanner.scan(chunk, SegmentedString(), preloads, resource->response().url());
+    }
+
+    if (preloads.size()) {
+        m_preloader->document()->loader()->didObserveLoadingBehavior(WebLoadingBehaviorFlag::WebLoadingBehaviorCSSPreloadFound);
+    }
+
+    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);
+    }
+}
+
 } // namespace blink