[android] Support full-screen on Cobalt.apk (#4327)

This CL sets URL field to GONE to support full-screen video on ATV, as
the layout of ContentShell.apk has a URL field.

b/362837382
b/372324497

cobalt/android/apk/app/src/main/java/dev/cobalt/coat/CobaltActivity.java

@@ -32,6 +32,7 @@
 import android.view.ViewGroup.LayoutParams;
 import android.view.ViewParent;
 import android.widget.FrameLayout;
+import android.widget.LinearLayout;
 import dev.cobalt.media.MediaCodecCapabilitiesLogger;
 import dev.cobalt.media.VideoSurfaceView;
 import dev.cobalt.util.DisplayUtil;
@@ -185,6 +186,8 @@ private void finishInitialization(Bundle savedInstanceState) {
           shellUrl = savedInstanceState.getString(ACTIVE_SHELL_URL_KEY);
       }
       mShellManager.launchShell(shellUrl);
+
+      toggleFullscreenMode(true);
   }
 
   // Initially copied from ContentShellActiviy.java
@@ -245,6 +248,11 @@ protected void setStartupUrl(String url) {
       mStartupUrl = url;
   }
 
+  protected void toggleFullscreenMode(boolean enterFullscreen) {
+    LinearLayout toolBar = (LinearLayout) findViewById(R.id.toolbar);
+    toolBar.setVisibility(enterFullscreen ? View.GONE : View.VISIBLE);
+  }
+
   // Initially copied from ContentShellActiviy.java
   @Override
   public void onActivityResult(int requestCode, int resultCode, Intent data) {