Show video layer in fullscreen for WebRTC

This change reverts some of the changes we did for fullscreen video on android.
For fullscreen video, we hide the video layer and only show the media controls.
However, in WebRTC case, the video frame, instead of a texture, contains all the pixel data.
And the video frame is painted directly onto the layer without the help of a surface texture/surface view.
As a result, we shouldn't hide the fullscreen video layer if the video is WebRTC.

Test: Since this just reverts the logic for certain fullscreen video on android, no test is added as desktop fullscreen video tests should cover the case.

BUG=417306

Review URL: https://codereview.chromium.org/690533002

git-svn-id: svn://svn.chromium.org/blink/trunk@184755 bbb929c8-8fbe-4397-9dbb-9b2b20218538