Add UMA to break down data usage by http/https and video/non_video

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 573a82fc85f79fa58b750b1d80785fba34266952..5d86ac2490fb801aee6351a755bee8ce6a1a9eb7 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -34301,6 +34301,21 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Net.HttpContentLength.Http" units="bytes">
+  <owner>ajo@chromium.org</owner>
+  <summary>Size of the response body for plain http responses.</summary>
+</histogram>
+
+<histogram name="Net.HttpContentLength.Https" units="bytes">

[Alexei Svitkine (slow), 2017/04/11 18:44:12]

Please use histogram_suffixes construct for these to avoid repetition. See the
top of the file for details on how to.

+  <owner>ajo@chromium.org</owner>
+  <summary>Size of the response body for https responses.</summary>
+</histogram>
+
+<histogram name="Net.HttpContentLength.Video" units="bytes">
+  <owner>ajo@chromium.org</owner>
+  <summary>Size of the response body for video responses.</summary>
+</histogram>
+
 <histogram name="Net.HttpContentLengthCacheable" units="bytes">
   <owner>bengr@chromium.org</owner>
   <summary>