Obsolete GCM.RegistrationSenderIdCount, extend GCM.LoadStatus

Stop recording the number of sender IDs used for creating a GCM
registration, as the data is no longer being used. Extend the LoadStatus
one as it reflects our ability to load an on-disk database, failure
within which would interfere with the entire system.

Bug: 1117108, 1088805
Change-Id: I6f4a90adb637df47b0b7d24f442fd5eb5021bc99
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2461317
Auto-Submit: Peter Beverloo <peter@chromium.org>
Reviewed-by: Richard Knoll <knollr@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Jian Li <jianli@chromium.org>
Commit-Queue: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816972}

components/gcm_driver/gcm_client_impl.cc

@@ -932,9 +932,6 @@ void GCMClientImpl::Register(
         senders.append(",");
       senders.append(*iter);
     }
-    UMA_HISTOGRAM_COUNTS_1M("GCM.RegistrationSenderIdCount",
-                            gcm_registration_info->sender_ids.size());
-
     request_handler.reset(new GCMRegistrationRequestHandler(senders));
     source_to_record = senders;
   }

tools/metrics/histograms/histograms_xml/gcm/histograms.xml

@@ -248,8 +248,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="GCM.LoadStatus" enum="GCMLoadStatus"
-    expires_after="2020-09-27">
-  <owner>jianli@chromium.org</owner>
+    expires_after="2021-03-01">
+  <owner>peter@chromium.org</owner>
+  <owner>knollr@chromium.org</owner>
   <summary>Status code of loading from the persistent GCM store.</summary>
 </histogram>
 
@@ -315,6 +316,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="GCM.RegistrationSenderIdCount" units="units"
     expires_after="M85">
+  <obsolete>
+    Removed 10/2020 because there no longer was a need for the data.
+  </obsolete>
   <owner>jianli@chromium.org</owner>
   <summary>Number of sender IDs specified in a registration request.</summary>
 </histogram>