Clean up dependencies for disk_cache histogram_macros.h.

net/disk_cache/backend_impl.cc

Index: net/disk_cache/backend_impl.cc
diff --git a/net/disk_cache/backend_impl.cc b/net/disk_cache/backend_impl.cc
index d10a19d9af09e76c553c99c9a54d07a0d8c30f6a..9adf5a84c7d9da18ce9ca1315ba45e6a76c1e94c 100644
--- a/net/disk_cache/backend_impl.cc
+++ b/net/disk_cache/backend_impl.cc
@@ -28,8 +28,9 @@
 #include "net/disk_cache/experiments.h"
 #include "net/disk_cache/file.h"
 
-// This has to be defined before including histogram_macros.h from this file.
-#define NET_DISK_CACHE_BACKEND_IMPL_CC_
+// Define BLOCKFILE_BACKEND_IMPL_OBJ to be a disk_cache::BackendImpl* in order

[rvargas (doing something else), 2014/02/11 19:41:48]

nit: I much prefer the original comment. It explain _why_ the include is here
rather than as part of the regular list of includes, without re-spelling what
the code already says.

The new comment "reads aloud" the code, mentions a symbol that is not evident
here (what is it, where is it, why it matters), and leaves the important part
out (this define is needed for the header that follows).

+// to use the CACHE_UMA histogram macro.
+#define BLOCKFILE_BACKEND_IMPL_OBJ this
 #include "net/disk_cache/histogram_macros.h"
 
 using base::Time;