Add histograms to ResourceFetcher to measure memory cache hit rate.

Source/core/fetch/Resource.h

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller <mueller@kde.org>
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
     version 2 of the License, or (at your option) any later version.
@@ skipping 40 matching lines @@
 // A resource that is held in the cache. Classes who want to use this object should derive
 // from ResourceClient, to get the function calls in case the requested data has arrived.
 // This class also does the actual communication with the loader to obtain the resource from the network.
 class Resource {
     WTF_MAKE_NONCOPYABLE(Resource); WTF_MAKE_FAST_ALLOCATED;
     friend class MemoryCache;
     friend class InspectorResource;
 
 public:
     enum Type {
-        MainResource,
+        MainResource = 0,

[abarth-chromium, 2013/09/13 17:38:18]

This change doesn't do anything.

[Philippe, 2013/09/16 11:47:21]

Done.

         Image,
         CSSStyleSheet,
         Script,
         Font,
         Raw,
         SVGDocument,
         XSLStyleSheet,
         LinkPrefetch,
         LinkSubresource,
         TextTrack,
         Shader,
-        ImportResource
+        ImportResource,
+        TypeBoundaryValue = 13, // Used for histograms.

[abarth-chromium, 2013/09/13 17:38:18]

What is TypeBoundaryValue?  Perhaps you mean NumberOfTypes?

Also, no need for this comment.  Folks can grep the code to see where this value
is used.

[Philippe, 2013/09/16 11:47:21]

Done.

     };
 
     enum Status {
         Unknown, // let cache decide what to do with it
         Pending, // only partially loaded
         Cached, // regular case
         LoadError,
         DecodeError
     };
 
@@ skipping 269 matching lines @@
     // If this field is non-null, the resource has a proxy for checking whether it is still up to date (see m_resourceToRevalidate).
     Resource* m_proxyResource;
 
     // These handles will need to be updated to point to the m_resourceToRevalidate in case we get 304 response.
     HashSet<ResourcePtrBase*> m_handlesToRevalidate;
 };
 
 }
 
 #endif