Add UMA histogram to track the various sources that request the feedback app

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 b76c0f691c5dc7b17c0ebe432d8391e841db8413..55ca852ceea7eb68a1b233f9d824d57d798ab8db 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -20821,6 +20821,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Feedback.RequestSource" enum="FeedbackSource">
+  <owner>afakhry@chromium.org</owner>
+  <summary>Records the source that requested showing the feedback app.</summary>
+</histogram>
+
 <histogram name="FileBrowser.CloudImport.UserAction"
     enum="CloudImportUserAction">
   <owner>smckay@google.com</owner>
@@ -97363,6 +97368,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="1969" label="ElementNameDOMValidHTMLParserInvalid"/>
 </enum>
 
+<enum name="FeedbackSource" type="int">
+  <int value="0" label="Arc App"/>
+  <int value="1" label="Ash"/>
+  <int value="2" label="Browser Command"/>
+  <int value="3" label="MD Settings About Page"/>
+  <int value="4" label="Old Settings About Page"/>
+  <int value="5" label="Profile Error Dialog"/>
+  <int value="6" label="SadTab Page"/>
+  <int value="7" label="Supervised User Interstitial"/>
+</enum>
+
 <enum name="FetchRequestMode" type="int">
   <int value="0" label="SameOrigin"/>
   <int value="1" label="NoCORS"/>