Add a feature which, when enabled, blocks permissions after X prompt dismissals.

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 6c66724ba8f81f7b7c752a6d53f91ffbce0483e5..0ca38136bc4ee48c7297cf0b08002cad33b5495e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -39289,6 +39289,16 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Permissions.DismissCount">
+  <owner>dominickn@chromium.org</owner>
+  <summary>
+    This metric tracks the total number of prompt dismissal events for an
+    origin, recorded at the time of a prompt dismissal. Repeated dismissals for
+    an origin will record a higher count in this histogram. The suffix of the
+    histogram indicates which particular permission.
+  </summary>
+</histogram>
+
 <histogram name="Permissions.Prompt.Accepted" enum="PermissionRequestType">
   <owner>benwells@chromium.org</owner>
   <owner>tsergeant@chromium.org</owner>
@@ -100080,6 +100090,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="Permissions.Action"/>
   <affected-histogram name="Permissions.Action.InsecureOrigin"/>
   <affected-histogram name="Permissions.Action.SecureOrigin"/>
+  <affected-histogram name="Permissions.DismissCount"/>
   <affected-histogram name="Permissions.Requested.CrossOrigin"/>
 </histogram_suffixes>