Set autoplay gesture override experiment based on finch trial group.

content/browser/renderer_host/render_view_host_impl.cc

Index: content/browser/renderer_host/render_view_host_impl.cc
diff --git a/content/browser/renderer_host/render_view_host_impl.cc b/content/browser/renderer_host/render_view_host_impl.cc
index 19033a8ecdfa24d7156bc34187e4d0aa82ada488..8e0cb9f838fb6c3555fdfddbc5acd4005e62ed13 100644
--- a/content/browser/renderer_host/render_view_host_impl.cc
+++ b/content/browser/renderer_host/render_view_host_impl.cc
@@ -445,6 +445,11 @@ WebPreferences RenderViewHostImpl::ComputeWebkitPrefs() {
   prefs.user_gesture_required_for_media_playback = !command_line.HasSwitch(
       switches::kDisableGestureRequirementForMediaPlayback) &&
           (autoplay_group_name.empty() || autoplay_group_name != "Enabled");
+
+  // Handle autoplay gesture override experiment.
+  // Note that anything but a well-formed string turns the experiment off.
+  prefs.autoplay_experiment_mode = base::FieldTrialList::FindFullName(
+      "MediaElementGestureOverrideExperiment");
 #endif
 
   prefs.touch_enabled = ui::AreTouchEventsEnabled();