Add metrics for coalesced permission prompts.

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 07be787606d0f1d911f763b55f01147541fb6828..810e530b18d11d5acc7714397966811438d918e7 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -35877,19 +35877,30 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
-<histogram name="Permissions.Prompt.Shown" enum="PermissionBubbleType">

[benwells, 2016/04/28 12:55:24]

I mistakenly left in this histogram description in a previous patch.

+<histogram name="Permissions.Prompt.MergedBubbleTypes"
+    enum="PermissionBubbleType">
   <owner>benwells@chromium.org</owner>
   <owner>tsergeant@chromium.org</owner>
   <summary>
-    Tracks how many times permission prompts are shown to users.
+    Tracks the permission bubble request types that are being merged into
+    coalesced bubbles.
+  </summary>
+</histogram>
+
+<histogram name="Permissions.Prompt.RequestsPerPrompt">
+  <owner>benwells@chromium.org</owner>
+  <owner>tsergeant@chromium.org</owner>
+  <summary>
+    How many permission requests each permissions prompt shown to the user
+    contains.
   </summary>
 </histogram>
 
-<histogram name="Permissions.Prompt.ShownForPermission" enum="PermissionType">
+<histogram name="Permissions.Prompt.Shown" enum="PermissionBubbleType">
   <owner>benwells@chromium.org</owner>
   <owner>tsergeant@chromium.org</owner>
   <summary>
-    Tracks how many times permission prompts for permissions are shown to users.
+    Tracks how many times permission prompts are shown to users.
   </summary>
 </histogram>