Add a new metric for how many times permissions prompts are shown.

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 c0923792afd5d271f2e3cceda5328edca6c1131a..03d8fdf5a78a7b6ae9835b0e18b80fc519d88ceb 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -35686,6 +35686,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Permissions.Prompt.Shown" enum="PermissionBubbleType">
+  <owner>benwells@chromium.org</owner>
+  <owner>tsergeant@chromium.org</owner>
+  <summary>
+    Tracks how many times permission prompts are shown to users.
+  </summary>
+</histogram>
+
 <histogram name="Permissions.Requested.CrossOrigin" enum="PermissionStatus">
   <owner>keenanb@google.com</owner>
   <owner>jww@chromium.org</owner>
@@ -80102,6 +80110,16 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="4" label="REVOKED"/>
 </enum>
 
+<enum name="PermissionBubbleType" type="int">
+  <int value="0" label="PERMISSION_BUBBLE_UNKNOWN"/>
+  <int value="1" label="PERMISSION_BUBBLE_MULTIPLE"/>
+  <int value="2" label="PERMISSION_BUBBLE_PERMISSION"/>
+  <int value="3" label="PERMISSION_BUBBLE_QUOTA"/>
+  <int value="4" label="PERMISSION_BUBBLE_DOWNLOAD"/>
+  <int value="5" label="PERMISSION_BUBBLE_MEDIA_STREAM"/>
+  <int value="6" label="PERMISSION_BUBBLE_REGISTER_PROTOCOL_HANDLER"/>
+</enum>
+
 <enum name="PermissionStatus" type="int">
   <int value="0" label="PERMISSION_STATUS_GRANTED"/>
   <int value="1" label="PERMISSION_STATUS_DENIED"/>
@@ -80109,7 +80127,7 @@ To add a new entry, add it with any value and run test to compute valid value.
 </enum>
 
 <enum name="PermissionType" type="int">
-  <int value="0" label="PERMISSION_UNKONWN"/>
+  <int value="0" label="PERMISSION_UNKNOWN"/>
   <int value="1" label="PERMISSION_MIDI_SYSEX"/>
   <int value="2" label="PERMISSION_PUSH_MESSAGING"/>
   <int value="3" label="PERMISSION_NOTIFICATIONS"/>