Push API: Refactor and fix unsubscribe API

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 cefb886771b4e2c82fbd8ee6fccca0b08d478a06..41c2fa86738c452f134853e09987886f31b27905 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -47782,11 +47782,20 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="PushMessaging.UnregistrationReason"
+    enum="PushUnregistrationReason">
+  <owner>johnme@google.com</owner>
+  <summary>
+    When unregistering a website from push messaging, this records the reason
+    why it is being unregistered.
+  </summary>
+</histogram>
+
 <histogram name="PushMessaging.UnregistrationStatus"
     enum="PushUnregistrationStatus">
   <owner>johnme@google.com</owner>
   <summary>
-    When a webpage unregisters from push messaging, this records whether the
+    When unregistering a website from push messaging, this records whether the
     request is successful, or otherwise the type of error encountered.
   </summary>
 </histogram>
@@ -93815,7 +93824,7 @@ value.
   <int value="0" label="Successful"/>
   <int value="1" label="Message was invalid"/>
   <int value="2" label="App id was unknown"/>
-  <int value="3" label="App no longer has permission"/>
+  <int value="3" label="Origin no longer has permission"/>
   <int value="4" label="Service Worker not found"/>
   <int value="5" label="Service Worker error"/>
   <int value="6" label="event.waitUntil promise rejected"/>
@@ -93846,6 +93855,14 @@ value.
   <int value="12" label="Empty or missing manifest"/>
 </enum>
 
+<enum name="PushUnregistrationReason" type="int">
+  <int value="0" label="JavaScript API"/>
+  <int value="1" label="Permission revoked"/>
+  <int value="2" label="Incoming message app id was unknown"/>
+  <int value="3" label="Incoming message origin no longer has permission"/>
+  <int value="4" label="Incoming message Service Worker not found"/>
+</enum>
+
 <enum name="PushUnregistrationStatus" type="int">
   <int value="0" label="Successful - from push service"/>
   <int value="1" label="Successful - was not registered"/>