Reland of Cache SubResourceIntegrity checks at Resource (patchset #2 id:20001 of https://codereview…

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

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All
     rights reserved.
     Copyright (C) 2009 Torch Mobile Inc. http://www.torchmobile.com/
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
@@ skipping 747 matching lines @@
 ResourceFetcher::determineRevalidationPolicy(Resource::Type type,
                                              const FetchRequest& fetchRequest,
                                              Resource* existingResource,
                                              bool isStaticData) const {
   const ResourceRequest& request = fetchRequest.resourceRequest();
 
   if (!existingResource)
     return Load;
 
   // Checks if the resource has an explicit policy about integrity metadata.
-  // Currently only applies to ScriptResources.
   //
-  // This is necessary because ScriptResource objects do not keep the raw data
-  // around after the source is accessed once, so if the resource is accessed
-  // from the MemoryCache for a second time, there is no way to redo an
-  // integrity check.
+  // This is necessary because ScriptResource and CSSStyleSheetResource objects
+  // do not keep the raw data around after the source is accessed once, so if
+  // the resource is accessed from the MemoryCache for a second time, there is
+  // no way to redo an integrity check.
   //
   // Thus, Blink implements a scheme where it caches the integrity information
-  // for a ScriptResource after the first time it is checked, and if there is
+  // for those resources after the first time it is checked, and if there is
   // another request for that resource, with the same integrity metadata, Blink
   // skips the integrity calculation. However, if the integrity metadata is a
   // mismatch, the MemoryCache must be skipped here, and a new request for the
   // resource must be made to get the raw data. This is expected to be an
   // uncommon case, however, as it implies two same-origin requests to the same
   // resource, but with different integrity metadata.
   RecordSriResourceIntegrityMismatchEvent(CheckingForIntegrityMismatch);
   if (existingResource->mustRefetchDueToIntegrityMetadata(fetchRequest)) {
     RecordSriResourceIntegrityMismatchEvent(RefetchDueToIntegrityMismatch);
     return Reload;
@@ skipping 806 matching lines @@
   visitor->trace(m_context);
   visitor->trace(m_archive);
   visitor->trace(m_loaders);
   visitor->trace(m_nonBlockingLoaders);
   visitor->trace(m_documentResources);
   visitor->trace(m_preloads);
   visitor->trace(m_resourceTimingInfoMap);
 }
 
 }  // namespace blink