Don't remove CSSPreloaderResourceClient for unused speculative markup preloads

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.
  *
  * Redistribution and use in source and binary forms, with or without
  * 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.
@@ skipping 302 matching lines @@
     m_preloader->takeAndPreload(preloads);
     DEFINE_STATIC_LOCAL(
         CustomCountHistogram, cssImportHistogram,
         ("PreloadScanner.ExternalCSS.PreloadCount", 1, 100, 50));
     cssImportHistogram.count(m_preloader->countPreloads() -
                              currentPreloadCount);
   }
 }
 
 void CSSPreloaderResourceClient::clearResource() {
+  // Do not remove the client for unused, speculative markup preloads. This will
+  // trigger cancellation of the request and potential removal from memory
+  // cache. Link preloads are an exception because they support dynamic removal
+  // cancelling the request (and have their own passive resource client).
+  // Note: Speculative preloads which remain unused for their lifetime will
+  // never have this client removed. This should be fine because we only hold
+  // weak references to the resource.
+  if (m_resource && m_resource->isUnusedPreload() &&
+      !m_resource->isLinkPreload()) {
+    return;
+  }
+
   if (m_resource)
     m_resource->removeClient(this);
   m_resource.clear();
 }
 
 DEFINE_TRACE(CSSPreloaderResourceClient) {
   visitor->trace(m_preloader);
   visitor->trace(m_resource);
   StyleSheetResourceClient::trace(visitor);
 }
 
 }  // namespace blink