Make CSSPreloaderResourceClient hold weak references to its resource

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 237 matching lines @@
   m_rule.clear();
   m_ruleValue.clear();
 }
 
 CSSPreloaderResourceClient::CSSPreloaderResourceClient(
     Resource* resource,
     HTMLResourcePreloader* preloader)
     : m_policy(preloader->document()->settings()->cssExternalScannerPreload()
                    ? ScanAndPreload
                    : ScanOnly),
-      m_preloader(preloader) {
-  DCHECK(resource->getType() == Resource::Type::CSSStyleSheet);
-  setResource(toCSSStyleSheetResource(resource),
-              Resource::DontMarkAsReferenced);
+      m_preloader(preloader),
+      m_resource(toCSSStyleSheetResource(resource)) {

[Yoav Weiss, 2016/10/27 21:59:49]

Can you bring back the DCHECK? 

[Charlie Harrison, 2016/10/27 22:34:01]

AFAICT the to<Resource> type casts do this already (actually, they
ASSERT_WITH_SECURITY_IMPLICATION).

+  m_resource->addClient(this);
 }
 
 CSSPreloaderResourceClient::~CSSPreloaderResourceClient() {}
 
 void CSSPreloaderResourceClient::setCSSStyleSheet(
     const String& href,
     const KURL& baseURL,
     const String& charset,
     const CSSStyleSheetResource*) {
   clearResource();
@@ skipping 41 matching lines @@
     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);
   }
 }
 
+void CSSPreloaderResourceClient::clearResource() {
+  if (m_resource)
+    m_resource->removeClient(this);
+  m_resource.clear();
+}
+
 DEFINE_TRACE(CSSPreloaderResourceClient) {
   visitor->trace(m_preloader);
-  ResourceOwner<CSSStyleSheetResource>::trace(visitor);
+  visitor->trace(m_resource);
+  StyleSheetResourceClient::trace(visitor);
 }
 
 }  // namespace blink