Fix fullscreen scaling in AppRTCMobile.

The surface view renderer size was set to match parent so it couldn't
adjust based on the frame size. The size is now set to wrap_content
which allows the renderer to adjust. The root element of the call
activity is changed to FrameLayout to allow the renderer to center.

requestLayout is added to SurfaceView setScalingType so onMeasure gets
called again.

BUG=webrtc:7901

Review-Url: https://codereview.webrtc.org/2978173002
Cr-Commit-Position: refs/heads/master@{#19073}

webrtc/sdk/android/api/org/webrtc/SurfaceViewRenderer.java

@@ -164,12 +164,14 @@ public class SurfaceViewRenderer
   public void setScalingType(RendererCommon.ScalingType scalingType) {
     ThreadUtils.checkIsOnMainThread();
     videoLayoutMeasure.setScalingType(scalingType);
+    requestLayout();
   }
 
   public void setScalingType(RendererCommon.ScalingType scalingTypeMatchOrientation,
       RendererCommon.ScalingType scalingTypeMismatchOrientation) {
     ThreadUtils.checkIsOnMainThread();
     videoLayoutMeasure.setScalingType(scalingTypeMatchOrientation, scalingTypeMismatchOrientation);
+    requestLayout();
   }
 
   /**