Add UMA metrics for root scroller intervention to track forcing passive breakage.

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 34d789c3cd1626a02af2bd255a6264a2dd5b4b5e..eacf667a32594f4557372af6635156d1369e3b11 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -12976,6 +12976,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Time to request a timestamp from the X server.</summary>
 </histogram>
 
+<histogram name="Event.PassiveForcedEventDispatchBreakage"
+    enum="PassiveForcedListenerResultType">
+  <owner>dtapuska@chromium.org</owner>
+  <summary>
+    Counts the number of event listener invocations that were forced to be
+    passive due to interventions and whether the invocation of the listener
+    called prevent default or not.

[tdresser, 2016/07/08 17:37:11]

Indicate that this is only recorded in cases where listener invocations were
forced passive.

[dtapuska, 2016/07/08 19:03:53]

does it not already say that?

[tdresser, 2016/07/08 19:09:50]

Uh, yeah, it says that exactly...
Nevermind...

+  </summary>
+</histogram>
+
 <histogram name="Event.PassiveListeners" enum="EventResultType">
   <owner>dtapuska@chromium.org</owner>
   <summary>
@@ -85191,6 +85201,11 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="3" label="Cookie contains both control chars and is invalid"/>
 </enum>
 
+<enum name="PassiveForcedListenerResultType" type="int">
+  <int value="0" label="PreventDefaultNotCalled"/>
+  <int value="1" label="DocumentLevelTouchPreventDefaultCalled"/>
+</enum>
+
 <enum name="PasswordBubbleDisplayDisposition" type="int">
   <int value="0" label="Opened automatically / Offering a password to save"/>
   <int value="1" label="Opened manually / Offering a password to save"/>