Preload scan external CSS for @import

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

Index: third_party/WebKit/Source/core/html/parser/HTMLResourcePreloader.cpp
diff --git a/third_party/WebKit/Source/core/html/parser/HTMLResourcePreloader.cpp b/third_party/WebKit/Source/core/html/parser/HTMLResourcePreloader.cpp
index 1b6b6692b68e02a2ccc20f5d2c95994136b22fde..6f3f5dfe78c820765d5df0abe6e7405a27544fd8 100644
--- a/third_party/WebKit/Source/core/html/parser/HTMLResourcePreloader.cpp
+++ b/third_party/WebKit/Source/core/html/parser/HTMLResourcePreloader.cpp
@@ -26,8 +26,10 @@
 #include "core/html/parser/HTMLResourcePreloader.h"
 
 #include "core/dom/Document.h"
+#include "core/fetch/CSSStyleSheetResource.h"
 #include "core/fetch/FetchInitiatorInfo.h"
 #include "core/fetch/ResourceFetcher.h"
+#include "core/frame/Settings.h"
 #include "core/loader/DocumentLoader.h"
 #include "platform/Histogram.h"
 #include "public/platform/Platform.h"
@@ -48,6 +50,14 @@ HTMLResourcePreloader* HTMLResourcePreloader::create(Document& document)
 DEFINE_TRACE(HTMLResourcePreloader)
 {
     visitor->trace(m_document);
+    visitor->trace(m_cssPreloaders);
+}
+
+int HTMLResourcePreloader::countPreloads()
+{
+    if (m_document->loader())
+        return m_document->loader()->fetcher()->countPreloads();
+    return 0;
 }
 
 static void preconnectHost(PreloadRequest* request, const NetworkHintsInterface& networkHintsInterface)
@@ -80,7 +90,19 @@ void HTMLResourcePreloader::preload(std::unique_ptr<PreloadRequest> preload, con
     int duration = static_cast<int>(1000 * (monotonicallyIncreasingTime() - preload->discoveryTime()));
     DEFINE_STATIC_LOCAL(CustomCountHistogram, preloadDelayHistogram, ("WebCore.PreloadDelayMs", 0, 2000, 20));
     preloadDelayHistogram.count(duration);
-    m_document->loader()->startPreload(preload->resourceType(), request);
+
+    Resource* resource = m_document->loader()->startPreload(preload->resourceType(), request);
+    // Note that if the cssExternalScanner{Preload,NoPreload} settings flags are
+    // not set, this resource client does nothing.
+    if (resource && preload->resourceType() == Resource::CSSStyleSheet) {
+        Settings* settings = m_document->settings();
+        if (!settings)
+            return;
+        if (!settings->cssExternalScannerNoPreload() && !settings->cssExternalScannerPreload()) {
+            return;
+        }
+        m_cssPreloaders.add(new CSSPreloaderResourceClient(resource, this));
+    }
 }
 
 } // namespace blink