Track size of files serialized by the JsonPrefStore.

In an effort to see what percentage of the population has exceedingly large pref files.

BUG=355722

Review URL: https://codereview.chromium.org/391893002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@283371 0039d316-1c4b-4281-b951-d872f2087c98

base/prefs/json_pref_store.cc

@@ -9,12 +9,15 @@
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/file_util.h"
+#include "base/files/file_path.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/message_loop/message_loop_proxy.h"
+#include "base/metrics/histogram.h"
 #include "base/prefs/pref_filter.h"
 #include "base/sequenced_task_runner.h"
+#include "base/strings/string_util.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "base/values.h"
 
@@ -388,7 +391,27 @@ bool JsonPrefStore::SerializeData(std::string* output) {
 
   JSONStringValueSerializer serializer(output);
   serializer.set_pretty_print(true);
-  return serializer.Serialize(*prefs_);
+  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;
 }
 
 void JsonPrefStore::FinalizeFileRead(bool initialization_successful,

tools/metrics/histograms/histograms.xml

@@ -27065,6 +27065,14 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Settings.JsonDataSizeKilobytes" units="KB">
+  <owner>gab@chromium.org</owner>
+  <summary>
+    The size of the JSON settings content about to be written to disk in
+    kilobytes. Suffixed with the name of the JSON file being written to disk.
+  </summary>
+</histogram>
+
 <histogram name="Settings.MigratedHashesFromLocalState" enum="BooleanMigrated">
   <owner>csharp@chromium.org</owner>
   <owner>gab@chromium.org</owner>
@@ -32647,6 +32655,16 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>Whether the scroll is executed on main thread.</summary>
 </histogram>
 
+<histogram name="UMA.ClientIdBackupRecoveredWithAge" units="hours">
+  <owner>gab@chromium.org</owner>
+  <summary>
+    Recorded when we are somehow missing the client ID stored in Local State yet
+    are able to recover it from a backup location along with the backed up
+    installation date. This report carries the age in hours of the recovered
+    client id.
+  </summary>
+</histogram>
+
 <histogram name="UMA.ClientIdMigrated" enum="BooleanMigrated">
   <owner>asvitkine@chromium.org</owner>
   <summary>
@@ -50563,6 +50581,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <affected-histogram name="Precache.Saved"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="PreferenceFileNames" separator=".">
+  <suffix name="Local_State" label="Local State file"/>
+  <suffix name="Preferences" label="Preferences file"/>
+  <suffix name="Secure_Preferences" label="Secure Preferences file"/>
+  <affected-histogram name="Settings.JsonDataSizeKilobytes"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="Prefetch">
   <suffix name="ContentPrefetchPrefetchOff"
       label="Prefetch is completely disabled."/>