Tracks GVR version crossed with headset type using UMA.

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 7b2303dccb9969dc8a781e8db719e9c50284764e..b9fcaa08a192267f02962d27227afa9550b8cb91 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -78791,6 +78791,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="VRRuntimeVersion.GVR" units="normalized version">

[rkaplow, 2017/05/25 20:57:27]

what is the space of possible versions here btw?

[tiborg, 2017/05/25 21:41:42]

At the moment there are 9 publicly released GVR versions we can log. But they
release new versions frequently. So, it's hard to predict. The versions are
between 1.0 to 1.60 (in encoded form 1000000 to 1060000).

+  <owner>tiborg@chromium.org</owner>
+  <summary>
+    The GVR version being used for VR. Special values: (-4) Could not encode GVR
+    version; (-3) Device does not support VR; (-2) GVR is not installed; (-1)
+    GVR is installed but version is too old to be logged.
+  </summary>
+</histogram>
+
 <histogram name="VRSessionNavigationCount">
   <owner>billorr@chromium.org</owner>
   <summary>
@@ -92116,6 +92125,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <affected-histogram name="WebRTC.Video.Encoded.Qp"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="VRRuntimeVersionGVRHeadset" separator=".">
+  <suffix name="Cardboard" label="GVR version used with Carboard."/>
+  <suffix name="Daydream" label="GVR version used with Daydream."/>
+  <suffix name="Unknown" label="GVR version used with an unknown headset."/>
+  <affected-histogram name="VRRuntimeVersion.GVR"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="VRSessionType" separator=".">
   <suffix name="Browser"
       label="The session is restricted to the period that the browser is