Record the tab state during 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 c32738ed925dc06bb79ce45ead7f9600071d7a4c..54ec1e0a08da17b99a10385d1d306b24ccb8e59f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -9362,6 +9362,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="DataUse.AppTabState" units="bytes">
+  <owner>rajendrant@chromium.org</owner>
+  <owner>bengr@chromium.org</owner>
+  <summary>
+    Records the data use of Chrome user traffic by the foregound vs. background
+    state of the app and tab.
+  </summary>
+</histogram>
+
 <histogram name="DataUse.BackgroundToDataRecievedPerByte" units="ms">
   <owner>rajendrant@chromium.org</owner>
   <owner>bengr@chromium.org</owner>
@@ -109155,6 +109164,16 @@ value.
   <affected-histogram name="DataUsage.ReportSubmission.Bytes"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="DataUse.AppTabState.Dimensions" separator=".">
+  <suffix name="Upstream.AppBackground"/>
+  <suffix name="Upstream.AppForeground.TabBackground"/>
+  <suffix name="Upstream.AppForeground.TabForeground"/>
+  <suffix name="Downstream.AppBackground"/>
+  <suffix name="Downstream.AppForeground.TabBackground"/>
+  <suffix name="Downstream.AppForeground.TabForeground"/>
+  <affected-histogram name="DataUse.AppTabState"/>

[RyanSturm, 2016/12/16 16:26:11]

I think it would be better to use an already existing affected-histogram. Does
DataUse.TrafficSize.User already measure this same thing not broken up by
direction, and state? If so you should just use that as the affected histogram
so that these would be "DataUse.TrafficSize.User.Upstream.AppBackground".

WDYT?

[Raj, 2016/12/16 19:59:11]

All existing histograms measure datause broken by direction, appstate, cellular.
For the tabstate, cellular is a don't care, which would reduce the number of
histograms. Is it performance/datause intensive to add new affected-histogram ?

[RyanSturm, 2016/12/19 19:31:49]

It is only expensive in the sense that histograms.xml gets bigger and you have
to write descriptions twice AFAIK.

If you add all of these suffixes to <histogram_suffixes
name="DataUse.Dimensions"> will there be a problem?

You should be able to have some suffixes track cellular and some track app state
in the same histogram_suffixes.

+</histogram_suffixes>
+
 <histogram_suffixes name="DataUse.Bytes" separator=".">
   <suffix name="Delegate" label="As reported by the network delegate."/>
   <suffix name="OS"