Add HttpCache histograms focussed on blocking and transaction type.

net/disk_cache/backend_impl.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // See net/disk_cache/disk_cache.h for the public interface of the cache.
 
 #ifndef NET_DISK_CACHE_BACKEND_IMPL_H_
 #define NET_DISK_CACHE_BACKEND_IMPL_H_
 
 #include "base/file_path.h"
@@ skipping 242 matching lines @@
   void TrimDeletedListForTest(bool empty);
 
   // Performs a simple self-check, and returns the number of dirty items
   // or an error code (negative value).
   int SelfCheck();
 
   // Ensures the index is flushed to disk (a no-op on platforms with mmap).
   void FlushIndex();
 
   // Backend implementation.
+  virtual net::CacheType GetCacheType() const OVERRIDE;
   virtual int32 GetEntryCount() const OVERRIDE;
   virtual int OpenEntry(const std::string& key, Entry** entry,
                         const CompletionCallback& callback) OVERRIDE;
   virtual int CreateEntry(const std::string& key, Entry** entry,
                           const CompletionCallback& callback) OVERRIDE;
   virtual int DoomEntry(const std::string& key,
                         const CompletionCallback& callback) OVERRIDE;
   virtual int DoomAllEntries(const CompletionCallback& callback) OVERRIDE;
   virtual int DoomEntriesBetween(const base::Time initial_time,
                                  const base::Time end_time,
@@ skipping 120 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(BackendImpl);
 };
 
 // Returns the preferred max cache size given the available disk space.
 NET_EXPORT_PRIVATE int PreferedCacheSize(int64 available);
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_BACKEND_IMPL_H_