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 e68768b38fb381ee83a42fa013bdd2d4de836e2e..0b8a38a8d5d13e182e96e8bbf405c3c394d75aff 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -54041,7 +54041,7 @@ 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"/>
@@ -54049,6 +54049,7 @@ 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">