Media Session: add metadata and action setters as ukm_features.

Bug: 1043219
Change-Id: If901e5edb0f3db7d25cea5bf7ed361e0ffe4cf56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2008248
Auto-Submit: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#733046}

components/page_load_metrics/browser/observers/use_counter/ukm_features.cc

@@ -147,6 +147,8 @@ UseCounterPageLoadMetricsObserver::GetAllowedUkmFeatures() {
               kV8VideoPlaybackQuality_CorruptedVideoFrames_AttributeGetter,
           WebFeature::kInputTypeCheckboxRenderedNonSquare,
           WebFeature::kInputTypeRadioRenderedNonSquare,
+          WebFeature::kV8MediaSession_Metadata_AttributeSetter,
+          WebFeature::kV8MediaSession_SetActionHandler_Method,
       }));
   return *opt_in_features;
 }