restricts when context could be retrieved.

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 050e4a0327200ee54f81593db486b9769f482d0e..6c5c0155d0fd0c730769529ff2efccf9161e721c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -3347,10 +3347,10 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
 <histogram name="AuthPolicy.TimeToRunKlist" units="ms">
   <owner>ljusten@chromium.org</owner>
   <summary>
-    Time in milliseconds to call 'klist' (print Kerberos ticket-granting-
-    ticket information). The command reveals a TGT's lifetime, which is used to
-    determine TGT status in GetUserStatus() called periodically by Chrome.
-    The value is recorded no matter if the operation was successful or not.
+    Time in milliseconds to call 'klist' (print Kerberos ticket-granting- ticket
+    information). The command reveals a TGT's lifetime, which is used to
+    determine TGT status in GetUserStatus() called periodically by Chrome. The
+    value is recorded no matter if the operation was successful or not.
   </summary>
 </histogram>
 
@@ -79824,6 +79824,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="VoiceInteraction.IllegalContextRequest">

[Ilya Sherman, 2017/05/25 22:21:16]

nit: Please add enum="BooleanHit".

[Muyuan, 2017/05/25 22:32:58]

Done.

+  <owner>muyuanli@chromium.org</owner>
+  <summary>
+    Counts the number of requests to retrieve voice interaction context when no
+    user interaction is initiated.
+  </summary>
+</histogram>
+
+<histogram name="VoiceInteraction.RequestArrivalSinceUserInteraction"

[Ilya Sherman, 2017/05/25 22:21:16]

Optional nit: I'd name this "UserInteractionToRequestArrivalDuration", or
possibly "Time" instead of "Duration", or possibly dropping the "Duration"
suffix altogether since it's a bit awkward and is clear enough from the units.

[Muyuan, 2017/05/25 22:32:58]

Done.

+    units="ms">
+  <owner>muyuanli@chromium.org</owner>
+  <summary>
+    Records the time between user interaction and the actual request arrival.
+  </summary>
+</histogram>
+
 <histogram name="VRDisplayPresentResult" enum="PresentationResult">
   <owner>billorr@chromium.org</owner>
   <summary>