Push API: Return cached registration if available.

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 b8852cd48e961f78bfb7b5b0ae5d7a7fecd7c104..07d4f882205709d36d6a6e6ef8a56a01a13a2272 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -53767,7 +53767,7 @@ To add a new entry, add it with any value and run test to compute valid value.
 </enum>
 
 <enum name="PushRegistrationStatus" type="int">
-  <int value="0" label="Successful"/>
+  <int value="0" label="Successful - from push service"/>
   <int value="1" label="Page has no active Service Worker"/>
   <int value="2" label="Push service not available"/>
   <int value="3" label="Registration limit reached"/>
@@ -53775,6 +53775,7 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="5" label="Push service error"/>
   <int value="6" label="No sender id provided"/>
   <int value="7" label="Storage error"/>
+  <int value="8" label="Successful - from cache"/>
 </enum>
 
 <enum name="QuicAddressMismatch" type="int">