Add use-counters for Client-Hints features

Source/core/fetch/FetchContext.h

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 41 matching lines @@
 enum FetchResourceType {
     FetchMainResource,
     FetchSubresource
 };
 
 class CORE_EXPORT FetchContext : public NoBaseWillBeGarbageCollectedFinalized<FetchContext> {
     WTF_MAKE_NONCOPYABLE(FetchContext);
 public:
     static FetchContext& nullInstance();
 
+    // To avoid a dependency on core/ we redefine fetch based UseCounter features here.
+    enum FetchUseCounterFeature {

[Nate Chapin, 2015/06/16 17:10:28]

It seems unfortunate to have this enum essentially duplicate the
UseCounter::Feature enum. Could we separate UseCounter::Feature from the rest of
UseCounter and only give core/fetch/ access to the enum?

+        ClientHintsDPR,
+        ClientHintsResourceWidth,
+        ClientHintsViewportWidth
+    };
+
     virtual ~FetchContext() { }
     DEFINE_INLINE_VIRTUAL_TRACE() { }
 
     virtual bool isLiveContext() { return false; }
+    virtual void count(FetchUseCounterFeature) { }
 
     virtual void addAdditionalRequestHeaders(ResourceRequest&, FetchResourceType);
     virtual void setFirstPartyForCookies(ResourceRequest&);
     virtual CachePolicy cachePolicy() const;
     virtual ResourceRequestCachePolicy resourceRequestCachePolicy(const ResourceRequest&, Resource::Type) const;
 
     virtual void dispatchDidChangeResourcePriority(unsigned long identifier, ResourceLoadPriority, int intraPriorityValue);
     virtual void dispatchWillSendRequest(unsigned long identifier, ResourceRequest&, const ResourceResponse& redirectResponse, const FetchInitiatorInfo& = FetchInitiatorInfo());
     virtual void dispatchDidLoadResourceFromMemoryCache(const ResourceRequest&, const ResourceResponse&);
     virtual void dispatchDidReceiveResponse(unsigned long identifier, const ResourceResponse&, ResourceLoader* = 0);
@@ skipping 28 matching lines @@
     virtual void addClientHintsIfNecessary(FetchRequest&);
     virtual void addCSPHeaderIfNecessary(Resource::Type, FetchRequest&);
 
 protected:
     FetchContext() { }
 };
 
 }
 
 #endif