Add UMA to net::BidirectionalStream

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 9cd12ae7cb4aa277d187580ca00b95e3dcc5f82d..e6e4304dbf8d9ae90c54f58c2c49887cb9b2e2c1 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -3614,6 +3614,32 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="BidirectionalStream.ReceivedBytes" units="bytes">
+  <owner>xunjieli@chromium.org</owner>
+  <summary>Number of bytes received over this stream.</summary>
+</histogram>
+
+<histogram name="BidirectionalStream.SentBytes" units="bytes">
+  <owner>xunjieli@chromium.org</owner>
+  <summary>Number of bytes sent over this stream.</summary>
+</histogram>
+
+<histogram name="BidirectionalStream.TimeToResponseEnd" units="microseconds">

[Ilya Sherman, 2016/08/08 22:26:37]

Are you sure that the units are microseconds and not milliseconds?  Ditto below.

[xunjieli, 2016/08/09 20:31:28]

Yes, these are microseconds, because base::TimeDelta is in microseconds.
See: https://cs.chromium.org/chromium/src/base/time/time.h?rcl=0&l=13

[Ilya Sherman, 2016/08/10 05:49:34]

I agree that base::TimeDelta internally uses microseconds as the most granular
representation.  However, UMA_HISTOGRAM_TIMES calls UMA_HISTOGRAM_CUSTOM_TIMES,
which calls FactoryTimeGet(), which records the time value in milliseconds,
rather than microseconds.  Apologies if I'm still misunderstanding something,
perhaps not noticing a slight variation in the macro you're using.

[xunjieli, 2016/08/11 12:50:40]

Done. Ah, I see. Thanks for explaining that! It is indeed milliseconds as you
pointed out.

+  <owner>xunjieli@chromium.org</owner>
+  <summary>
+    How long it takes from starting the request to receiving the end of the
+    response.
+  </summary>
+</histogram>
+
+<histogram name="BidirectionalStream.TimeToResponseStart" units="microseconds">
+  <owner>xunjieli@chromium.org</owner>
+  <summary>
+    How long it takes from starting the request to receiving the start of
+    response.

[Ilya Sherman, 2016/08/08 22:26:37]

nit: s/of response/of the response

[xunjieli, 2016/08/11 12:50:40]

Done.

+  </summary>
+</histogram>
+
 <histogram name="Blacklist.Blocked" enum="DllHash">
   <owner>csharp@chromium.org</owner>
   <summary>
@@ -96169,6 +96195,17 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="WebRTC.Stun.BatchSuccessPercent.UnknownNAT"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="BidirectionalStreamExperiment" separator="."
+    ordering="prefix">
+  <owner>xunjieli@chromium.org</owner>
+  <suffix name="QUIC" label="Bidirectional streams that use QUIC protocol"/>
+  <suffix name="HTTP2" label="Bidirectional stream that use HTTP2 protocol"/>
+  <affected-histogram name="BidirectionalStream.ReceivedBytes"/>
+  <affected-histogram name="BidirectionalStream.SentBytes"/>
+  <affected-histogram name="BidirectionalStream.TimeToResponseEnd"/>
+  <affected-histogram name="BidirectionalStream.TimeToResponseStart"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="BlinkCanvasDrawImageType" separator=".">
   <suffix name="Canvas"/>
   <suffix name="ImageBitmap"/>