Reorganize net/disk_cache into backend specific directories.

net/disk_cache/blockfile/histogram_macros.h

Index: net/disk_cache/blockfile/histogram_macros.h
diff --git a/net/disk_cache/histogram_macros.h b/net/disk_cache/blockfile/histogram_macros.h
similarity index 96%
rename from net/disk_cache/histogram_macros.h
rename to net/disk_cache/blockfile/histogram_macros.h
index 6af9ca18ebe350a6f4dc684b1a3c39fa8e3ac380..a5d6f56f5c10ca888b78c97e5c4cb8ac6793d24b 100644
--- a/net/disk_cache/histogram_macros.h
+++ b/net/disk_cache/blockfile/histogram_macros.h
@@ -8,8 +8,8 @@
 // keeping track of a potentially large number of histogram objects that have to
 // survive the backend object that created them.
 
-#ifndef NET_DISK_CACHE_HISTOGRAM_MACROS_H_
-#define NET_DISK_CACHE_HISTOGRAM_MACROS_H_
+#ifndef NET_DISK_CACHE_BLOCKFILE_HISTOGRAM_MACROS_H_
+#define NET_DISK_CACHE_BLOCKFILE_HISTOGRAM_MACROS_H_
 
 // -----------------------------------------------------------------------------
 
@@ -119,4 +119,4 @@
     }\
   }
 
-#endif  // NET_DISK_CACHE_HISTOGRAM_MACROS_H_
+#endif  // NET_DISK_CACHE_BLOCKFILE_HISTOGRAM_MACROS_H_