Log pref file size histogram on read rather than on write.

base/prefs/json_pref_store.cc

Index: base/prefs/json_pref_store.cc
diff --git a/base/prefs/json_pref_store.cc b/base/prefs/json_pref_store.cc
index e35ed295d699b68ffe50d707d1864b8dcc046125..6eb3188e82f4afc3f2239f9389b50d7d0110e78b 100644
--- a/base/prefs/json_pref_store.cc
+++ b/base/prefs/json_pref_store.cc
@@ -8,12 +8,10 @@
 
 #include "base/bind.h"
 #include "base/callback.h"
-#include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/memory/ref_counted.h"
-#include "base/metrics/histogram.h"
 #include "base/prefs/pref_filter.h"
 #include "base/sequenced_task_runner.h"
 #include "base/strings/string_util.h"
@@ -99,11 +97,15 @@ scoped_ptr<JsonPrefStore::ReadResult> ReadPrefsFromDisk(
     base::Move(alternate_path, path);
   }
 
+  std::string histogram_suffix;
+  base::ReplaceChars(path.BaseName().MaybeAsASCII(), " ", "_",
+                     &histogram_suffix);
+
   int error_code;
   std::string error_msg;
   scoped_ptr<JsonPrefStore::ReadResult> read_result(
       new JsonPrefStore::ReadResult);
-  JSONFileValueSerializer serializer(path);
+  JSONFileValueSerializer serializer(path, histogram_suffix);
   read_result->value.reset(serializer.Deserialize(&error_code, &error_msg));
   read_result->error =
       HandleReadErrors(read_result->value.get(), path, error_code, error_msg);
@@ -379,27 +381,7 @@ bool JsonPrefStore::SerializeData(std::string* output) {
 
   JSONStringValueSerializer serializer(output);
   serializer.set_pretty_print(true);
-  bool result = serializer.Serialize(*prefs_);
-
-  if (result) {
-    std::string spaceless_basename;
-    base::ReplaceChars(path_.BaseName().MaybeAsASCII(), " ", "_",
-                       &spaceless_basename);
-
-    // The histogram below is an expansion of the UMA_HISTOGRAM_COUNTS_10000
-    // macro adapted to allow for a dynamically suffixed histogram name.
-    // Note: The factory creates and owns the histogram.
-    base::HistogramBase* histogram =
-        base::LinearHistogram::FactoryGet(
-            "Settings.JsonDataSizeKilobytes." + spaceless_basename,
-            1,
-            10000,
-            50,
-            base::HistogramBase::kUmaTargetedHistogramFlag);
-    histogram->Add(static_cast<int>(output->size()) / 1024);
-  }
-
-  return result;
+  return serializer.Serialize(*prefs_);
 }
 
 void JsonPrefStore::FinalizeFileRead(bool initialization_successful,