Reorganize net/disk_cache into backend specific directories.

net/disk_cache/blockfile/stats_histogram.h

Index: net/disk_cache/blockfile/stats_histogram.h
diff --git a/net/disk_cache/stats_histogram.h b/net/disk_cache/blockfile/stats_histogram.h
similarity index 90%
rename from net/disk_cache/stats_histogram.h
rename to net/disk_cache/blockfile/stats_histogram.h
index 2e481f52e424144001ddd00ca09961c084820906..8b9c8593252827c4d0d7a1e8d2a1cf03d3fdf4c6 100644
--- a/net/disk_cache/stats_histogram.h
+++ b/net/disk_cache/blockfile/stats_histogram.h
@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#ifndef NET_DISK_CACHE_STATS_HISTOGRAM_H_
-#define NET_DISK_CACHE_STATS_HISTOGRAM_H_
+#ifndef NET_DISK_CACHE_BLOCKFILE_STATS_HISTOGRAM_H_
+#define NET_DISK_CACHE_BLOCKFILE_STATS_HISTOGRAM_H_
 
 #include <string>
 
@@ -55,4 +55,4 @@ class StatsHistogram : public base::Histogram {
 
 }  // namespace disk_cache
 
-#endif  // NET_DISK_CACHE_STATS_HISTOGRAM_H_
+#endif  // NET_DISK_CACHE_BLOCKFILE_STATS_HISTOGRAM_H_