Force events to be non blocking if main thread is unresponsive.

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 543fa7e2cc5986675dd7fe8705bbb80713bfbfd2..82c675a4ff2a7c0f8c469196d5f98604cf97ef3c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -14944,10 +14944,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
     units="microseconds">
   <owner>dtapuska@chromium.org</owner>
   <summary>
-    Time between when a forced non-blocking touchstart or first touchmove event
-    per scroll was generated and the event processed during fling. This
-    histogram tracks the benefit of forcing non-blocking events listeners during
-    fling.
+    Time between when a touchstart or first touchmove event per scroll was
+    generated and the event processed, for events which were forced non-blocking
+    since they occurred during fling. This histogram tracks the benefit of
+    forcing events non-blocking during fling.
+  </summary>
+</histogram>
+
+<histogram
+    name="Event.PassiveListeners.ForcedNonBlockingLatencyDueToUnresponsiveMainThread"
+    units="microseconds">
+  <owner>tdresser@chromium.org</owner>
+  <summary>
+    Time between when a touchstart or first touchmove event per scroll was
+    generated and the event processed, for events which were forced non-blocking
+    since they occurred while the main thread was unresponsive. This histogram
+    tracks the benefit of forcing events non-blocking during fling.

[Ilya Sherman, 2016/12/16 00:46:02]

nit: I think you meant something about unresponsive main thread, rather than
"during fling", on this line?

[tdresser, 2016/12/16 13:32:43]

Done.

   </summary>
 </histogram>
 
@@ -83626,7 +83638,8 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="2" label="Suppressed"/>
   <int value="3" label="Cancelable and not canceled"/>
   <int value="4" label="Cancelable and canceled"/>
-  <int value="5" label="Forced Non-Blocking"/>
+  <int value="5" label="Forced Non-Blocking Due to Fling"/>
+  <int value="6" label="Forced Non-Blocking Due to Unresponsive Main Thread"/>
 </enum>
 
 <enum name="EventTimestampValidity" type="int">