Do not use overlays when VR shell is enabled.

media/blink/webmediaplayer_impl.h

Index: media/blink/webmediaplayer_impl.h
diff --git a/media/blink/webmediaplayer_impl.h b/media/blink/webmediaplayer_impl.h
index 6e01840d71c6e0e05129c139d91354fd04f2f4d9..19e31ebcedee0f480ff32c7720473653c366ade1 100644
--- a/media/blink/webmediaplayer_impl.h
+++ b/media/blink/webmediaplayer_impl.h
@@ -207,6 +207,7 @@ class MEDIA_BLINK_EXPORT WebMediaPlayerImpl
                                     PipelineStatus status);
   gfx::Size GetCanvasSize() const;
   void SetDeviceScaleFactor(float scale_factor);
+  void SetDisableFullscreenOverlays(bool disable_overlays);

[liberato (no reviews please), 2016/12/13 23:03:29]

SetDisable is a little confusing.  SetAllowFullscreenOverlays(bool) might be
better.

also worth a comment that this is set by default during construction, and one
probably doesn't want to call it except for VR.  it'll screw up the experiment
results that are attached to kForceVideoOverlays if it's called too much.

actually, maybe DisableFullScreenOverlaysForVR() is a better name, so it's super
clear that one should not call this unless one is you. :) 

[amp, 2016/12/13 23:40:02]

I'm leaning towards SetAllowFullscreenOverlays and checking both features
instead of doing anything in the constructor.

I'm looking into if we can signal finch when the experiment data is invalid
because of vr shell.

[amp, 2016/12/14 00:04:51]

Yes it is possible to make finch ignore data when vr shell is enabled.  See
cl/141952159

   void setPoster(const blink::WebURL& poster) override;
   void SetUseFallbackPath(bool use_fallback_path);
 #endif