Avoid double download for late discovered link preload resources.

third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp

Index: third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
diff --git a/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp b/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
index 0f6d48e7f03d9bf7106e1804c5d685c7c4f9617b..caa10e3692c9b015e3ebcb0a41efedc20d8daacb 100644
--- a/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
+++ b/third_party/WebKit/Source/core/fetch/ResourceFetcher.cpp
@@ -181,7 +181,7 @@ ResourceFetcher::ResourceFetcher(FetchContext* context)
 ResourceFetcher::~ResourceFetcher()
 {
 #if !ENABLE(OILPAN)
-    clearPreloads();
+    clearPreloads(ClearAllPreloads);
 #endif
 }
 
@@ -834,7 +834,7 @@ bool ResourceFetcher::isPreloaded(const KURL& url) const
     return false;
 }
 
-void ResourceFetcher::clearPreloads()
+void ResourceFetcher::clearPreloads(ClearPreloadsPolicy policy)
 {
 #if PRELOAD_DEBUG
     printPreloadStats();
@@ -845,7 +845,8 @@ void ResourceFetcher::clearPreloads()
     for (auto resource : *m_preloads) {
         resource->decreasePreloadCount();
         bool deleted = resource->deleteIfPossible();
-        if (!deleted && resource->preloadResult() == Resource::PreloadNotReferenced)
+        // avoidBlockingOnLoad is only set on non speculative preloads (i.e. <link rel=preload> triggered preloads)
+        if (!deleted && resource->preloadResult() == Resource::PreloadNotReferenced && (policy == ClearAllPreloads || !resource->avoidBlockingOnLoad()))
             memoryCache()->remove(resource.get());
     }
     m_preloads.clear();