Track size of files serialized by the JsonPrefStore.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index eeaab506a61b8261dbfb6b575afd0e25d98a25c8..a03f22883f857265a91822e6119e9ca2ba11c03f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -26955,6 +26955,14 @@ 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>
@@ -32528,6 +32536,16 @@ 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>
@@ -50371,6 +50389,13 @@ 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."/>