[Sync] Finch Experiment : Enable compression between sync client and server

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 e16727c2aa6bed7f73d2ba3fc283b9ad22979c3b..28ab7d9da8edb5ed5753baf888dc4f26ada82d4b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -44682,12 +44682,44 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Sync.RequestContentLengthCompressed" units="byte">

[Alexei Svitkine (slow), 2015/08/03 18:12:30]

Nit: For readability, suggest slight name tweak to:

Sync.RequestContentLength.Compressed
and:
Sync.RequestContentLength.Original

Also, units is usually plural, so byte -> bytes.

Same for the other pair.

[Gang Wu, 2015/08/04 22:14:00]

Done.

+  <owner>gangwu@chromium.org</owner>
+  <summary>
+    The request content size for a single HTTP/HTTPS call from sync client to
+    server. The content is compressed by gzip.
+  </summary>
+</histogram>
+
+<histogram name="Sync.RequestContentLengthOriginal" units="byte">
+  <owner>gangwu@chromium.org</owner>
+  <summary>
+    The original request content size for a single HTTP/HTTPS call from sync
+    client to server. It is the size before content got compressed.
+  </summary>
+</histogram>
+
 <histogram name="Sync.ResolveSimpleConflict"
     enum="SyncSimpleConflictResolutions">
   <owner>zea@chromium.org</owner>
   <summary>Enumeration of types of simple conflict resolutions.</summary>
 </histogram>
 
+<histogram name="Sync.ResponseContentLengthCompressed" units="byte">
+  <owner>gangwu@chromium.org</owner>
+  <summary>
+    The response content size for a single HTTP/HTTPS call from sync server to
+    client. The content is compressed by gzip.
+  </summary>
+</histogram>
+
+<histogram name="Sync.ResponseContentLengthOriginal" units="byte">
+  <owner>gangwu@chromium.org</owner>
+  <summary>
+    The original response content size for a single HTTP/HTTPS call from sync
+    server and client. It is the size after content got uncompressed.
+  </summary>
+</histogram>
+
 <histogram name="Sync.RestoreBackendInitializeSucess" enum="BooleanSuccess">
   <obsolete>
     Deprecated 11/2011.  Was counted incorrectly.  Replaced by