Record the time since Chromium is in background for background data use

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 2fbf786d0720efecba1eb895f1f01878170ba92b..4acaaef39ade09eb4157456fb846bd7799510df1 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -8803,6 +8803,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="DataUse.BackgroundDownstreamBytes" units="ms">

[Steven Holte, 2016/10/17 21:35:16]

This is a bit confusingly named, since from the name I would expect it to be
just a histogram of #of bytes recorded in background.

Maybe BackgroundToDataRecievedPerByte ?

[Raj, 2016/10/19 20:07:20]

Done.

+  <owner>rajendrant@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    The time since Chrome is in background when background data use happens.
+    Recorded for each byte of background data use. The source of traffic whether
+    from user browsing or chrome services is added as suffix to this histogram.
+  </summary>
+</histogram>
+
 <histogram name="DataUse.BytesReceived" units="bytes">
   <owner>tbansal@chromium.org</owner>
   <summary>Count of total bytes received by the Chrome on the network.</summary>
@@ -8813,6 +8823,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Count of total bytes sent by the Chrome on the network.</summary>
 </histogram>
 
+<histogram name="DataUse.FirstBackgroundDownstream" units="ms">

[Steven Holte, 2016/10/17 21:35:16]

Maybe name it BackgroundToFirstDownstream to better indicate that it is a
latency histogram.

[Raj, 2016/10/19 20:07:20]

Done.

+  <owner>rajendrant@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    The time since Chrome is in background when first background data use
+    happens. Recorded when first background downstream data use after Chrome is
+    in background. The source of traffic whether from from user browsing or

[Steven Holte, 2016/10/17 21:35:16]

from from?

[Raj, 2016/10/19 20:07:20]

Done.

+    chrome services is added as suffix to this histogram.

[Steven Holte, 2016/10/17 21:35:16]

Missing change to histogram_suffixes?

[Raj, 2016/10/19 20:07:20]

Done.

+  </summary>
+</histogram>
+
 <histogram name="DataUse.MessageSize" units="bytes">
   <owner>amohammadkhan@chromium.org</owner>
   <owner>bengr@chromium.org</owner>