Add histogram to measure string response size of URLFetcher.

BUG=101929
TEST=URLFetcher*Test.*


Review URL: http://codereview.chromium.org/8416001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@107780 0039d316-1c4b-4281-b951-d872f2087c98

content/common/net/url_fetcher_impl.cc

@@ -14,6 +14,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop_proxy.h"
+#include "base/metrics/histogram.h"
 #include "base/platform_file.h"
 #include "base/stl_util.h"
 #include "base/string_util.h"
@@ -1066,6 +1067,9 @@ bool URLFetcherImpl::GetResponseAsString(
     return false;
 
   *out_response_string = core_->data_;
+  UMA_HISTOGRAM_MEMORY_KB("UrlFetcher.StringResponseSize",
+                          (core_->data_.length() / 1024));
+
   return true;
 }