Add HttpCache histograms focussed on blocking and transaction type.

net/disk_cache/disk_cache.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.
 
 // Defines the public interface of the disk cache. For more details see
 // http://dev.chromium.org/developers/design-documents/network-stack/disk-cache
 
 #ifndef NET_DISK_CACHE_DISK_CACHE_H_
 #define NET_DISK_CACHE_DISK_CACHE_H_
 
@@ skipping 49 matching lines @@
   typedef net::CompletionCallback CompletionCallback;
 
   // If the backend is destroyed when there are operations in progress (any
   // callback that has not been invoked yet), this method cancels said
   // operations so the callbacks are not invoked, possibly leaving the work
   // half way (for instance, dooming just a few entries). Note that pending IO
   // for a given Entry (as opposed to the Backend) will still generate a
   // callback from within this method.
   virtual ~Backend() {}
 
+  // Returns the type of this cache.
+  virtual net::CacheType GetCacheType() const = 0;
+
   // Returns the number of entries in the cache.
   virtual int32 GetEntryCount() const = 0;
 
   // Opens an existing entry. Upon success, |entry| holds a pointer to an Entry
   // object representing the specified disk cache entry. When the entry pointer
   // is no longer needed, its Close method should be called. The return value is
   // a net error code. If this method returns ERR_IO_PENDING, the |callback|
   // will be invoked when the entry is available. The pointer to receive the
   // |entry| must remain valid until the operation completes.
   virtual int OpenEntry(const std::string& key, Entry** entry,
@@ skipping 218 matching lines @@
   // Note: This method is deprecated.
   virtual int ReadyForSparseIO(const CompletionCallback& callback) = 0;
 
  protected:
   virtual ~Entry() {}
 };
 
 }  // namespace disk_cache
 
 #endif  // NET_DISK_CACHE_DISK_CACHE_H_