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 15a5aaf1d36714052c7ccaf8db2548737a75454c..639d87a4919e7964b358a673d6d3fb2ec4374691 100644
--- a/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp
+++ b/third_party/WebKit/Source/core/html/parser/CSSPreloadScanner.cpp
@@ -27,8 +27,11 @@
 
 #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 {
@@ -233,4 +236,33 @@ void CSSPreloadScanner::emitRule(const SegmentedString& source)
     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::didAppendData(const CSSStyleSheetResource* resource)
+{
+    const String& chunk = resource->decodedText();

[kouhei (in TOK), 2016/04/21 06:35:03]

Sorry, I was surprised to know that decodedText() is const member func.
decodedText() shouldn't be const, as it actually mutates TextResource internal
state. Let me fix this in separate CL.

[kouhei (in TOK), 2016/04/24 22:26:22]

Hmm, thinking this over again, TextResource::decodedText modifies its
TextResourceDecoder state, but it always flush()s it in the end to get it back
to its initial state.

Let me retract the previous comment.

[Charlie Harrison, 2016/04/25 15:14:34]

Ack. Thanks for looking into this.

+    if (!chunk.isNull() && m_preloader) {
+        CSSPreloadScanner cssPreloadScanner;
+        PreloadRequestStream preloads;
+        // TODO(csharrison): Should SegmentedString be populated?
+        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