Fix overzealous DCHECK

Bug: 969023
Change-Id: Ibdb78ffc2bc4357be6ba059618e37e323d05fa56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1638006Reviewed-by: Bill Orr <billorr@chromium.org>
Commit-Queue: Piotr Bialecki <bialpio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#665269}

chrome/browser/vr/metrics/session_metrics_helper.cc

@@ -355,11 +355,10 @@ void SessionMetricsHelper::ReportRequestPresent(
     case Mode::kVrBrowsing:
     case Mode::kVrBrowsingRegular:
     case Mode::kVrBrowsingFullscreen:
+    case Mode::kWebXrVrPresentation:
       RecordPresentationStartAction(
           PresentationStartAction::kRequestFromVrBrowsing, options);
       return;
-    case Mode::kWebXrVrPresentation:
-      break;
   }
 
   NOTREACHED();