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 3670e9d20f50d763404c55cd8b62b1dead75b309..8e1914e305e31d2dca4ce77772ab13935cba980e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -60633,6 +60633,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>How long it takes the swap ack to return after a swap.</summary>
 </histogram>
 
+<histogram name="Scheduling.VsyncToBeginMainFrameLatency2" units="microseconds">

[Ilya Sherman, 2017/03/14 21:32:11]

Hmm, is it useful to include a "2" in this metric name?  I do see that the macro
you used does so... but I wonder whether that's really working as intended.

[stanisc, 2017/03/14 21:43:33]

My understanding is that the macro was changed at some point to collect metrics
in a more data bandwidth efficient way and "2" was appended to all metric names
at that point by changing the macro. For this new metric appending "2" obviously
isn't very useful, but I didn't want to duplicate the macro just for this one
metric. At least it is consistent with all other scheduler metrics.

I verified that it works as intended locally by looking at chrome://histograms.

+  <owner>stanisc@chromium.org</owner>
+  <summary>
+    The time from v-sync to when the main side actually starts the
+    BeginMainFrame.
+  </summary>
+</histogram>
+
 <histogram name="ScreenLocker.AuthenticationFailure" enum="UnlockType">
   <owner>sammiequon@chromium.org</owner>
   <summary>
@@ -115142,6 +115150,7 @@ from previous Chrome versions.
   <affected-histogram name="Scheduling.PrepareTilesDuration2"/>
   <affected-histogram name="Scheduling.SwapAckWasFast"/>
   <affected-histogram name="Scheduling.SwapToAckLatency2"/>
+  <affected-histogram name="Scheduling.VsyncToBeginMainFrameLatency2"/>
 </histogram_suffixes>
 
 <histogram_suffixes name="CompositorTimingHistoryProcess2" separator="."