Added UMA statistics for changing the active window via click or touch events.

tools/metrics/actions/actions.xml

Index: tools/metrics/actions/actions.xml
diff --git a/tools/metrics/actions/actions.xml b/tools/metrics/actions/actions.xml
index 0990180eeba760cd72bda8669dec39d28f30bdaf..87bcdd418b135df7dc40c1535c8ff98738ffbc6f 100644
--- a/tools/metrics/actions/actions.xml
+++ b/tools/metrics/actions/actions.xml
@@ -2501,6 +2501,15 @@ should be able to be added at any place in this file.
   <description>Please enter the description of this user action.</description>
 </action>
 
+<action name="Desktop_SwitchTask">
+  <owner>bruthig@google.com</owner>
+  <owner>tdanderson@google.com</owner>
+  <description>
+    Recorded when the user activates an existing task by clicking or tapping on

[tdanderson, 2015/06/04 22:15:51]

Specify this is only recorded for tasks which are windows.

[bruthig, 2015/06/05 17:28:21]

Done.

+    it in the 2-dimensional screen space.

[Alexei Svitkine (slow), 2015/06/04 18:16:04]

I find this action description pretty confusing. I think this needs some context
- i.e. that this action is ChromeOS specific and related to the task switcher.
(Also not sure why you mention "2-dimensional screen space" ... as opposed to
what?)

[tdanderson, 2015/06/04 22:15:51]

Would it be clearer if "in the 2-dimensional screen space" were omitted enirely?
Whatever change is made to the description here should be applied to the other
documentation in this CL.

[bruthig, 2015/06/05 17:28:21]

Attempted to make it better.

+  </description>
+</action>
+
 <action name="Destination_Application_Edit">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <description>Please enter the description of this user action.</description>