Record the number of loaded profiles when a profile is erased from the...

Record the number of loaded profiles when a profile is erased from the profiles map kept by profile manager.

The reason behind is, UMA is observing a significant amount of times when GetLoadedProfiles returns an empty list (multiple times during one session). We hope that recording such a histogram would help to find out the reason for it, or at least eliminate one possibility.

BUG=412794

Review URL: https://codereview.chromium.org/605333002

Cr-Commit-Position: refs/heads/master@{#297204}

chrome/browser/profiles/profile_manager.cc

@@ -949,6 +949,9 @@ void ProfileManager::OnProfileCreated(Profile* profile,
   } else {
     profile = NULL;
     profiles_info_.erase(iter);
+    // TODO(yiyaoliu): This is temporary, remove it after it's not used.
+    UMA_HISTOGRAM_COUNTS_100("UMA.ProfilesCount.AfterErase",
+                             profiles_info_.size());
   }
 
   if (profile) {

tools/metrics/histograms/histograms.xml

@@ -35569,6 +35569,15 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="UMA.ProfilesCount.AfterErase">
+  <owner>asvitkine@chromium.org</owner>
+  <owner>yiyaoliu@chromium.org</owner>
+  <summary>
+    Record the number of loaded profiles when a profile is erased from the
+    profiles map kept by profile manager.
+  </summary>
+</histogram>
+
 <histogram name="UMA.ProfileSignInStatus" enum="ProfileSigninStatus">
   <owner>asvitkine@chromium.org</owner>
   <owner>yiyaoliu@chromium.org</owner>