[Chromecast] Fix the flashing page when destroy web content

There is a flashing page when transiting from one cast app to
another cast app or when stopping a cast app. It is caused by redrawing
the webcontent view when destroying the WebContents.

Bug: internal b/79172781 b/79694573

Test: manually tested on Jasper

Change-Id: Ib445301a1f0d2a79cdf5a7dd2652a0666c570f06
Reviewed-on: https://chromium-review.googlesource.com/1132622Reviewed-by: Simeon Anfinrud <sanfin@chromium.org>
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Zhiheng(Vincent) Li <vincentli@google.com>
Cr-Commit-Position: refs/heads/master@{#574794}

chromecast/browser/android/apk/src/org/chromium/chromecast/shell/CastWebContentsFragment.java

@@ -66,6 +66,7 @@ public class CastWebContentsFragment extends Fragment {
             mFragmentRootView = inflater.cloneInContext(getContext())
                                         .inflate(R.layout.cast_web_contents_activity, null);
         }
+        mFragmentRootView.setVisibility(View.VISIBLE);
         return mFragmentRootView;
     }
 
@@ -117,10 +118,6 @@ public class CastWebContentsFragment extends Fragment {
     public void onResume() {
         Log.d(TAG, "onResume");
         super.onResume();
-        // Delayed set mFragmentRootView to visible to avoid activity UI -> one frame of fragment
-        // background -> cast app rendered UI
-        mFragmentRootView.setVisibility(View.INVISIBLE);
-        mFragmentRootView.postDelayed(this ::setToVisible, 150);
         mResumedState.set(Unit.unit());
     }
 

chromecast/browser/android/apk/src/org/chromium/chromecast/shell/CastWebContentsView.java

@@ -5,6 +5,7 @@
 package org.chromium.chromecast.shell;
 
 import android.content.Context;
+import android.graphics.drawable.ColorDrawable;
 import android.widget.FrameLayout;
 
 import org.chromium.chromecast.base.ScopeFactory;
@@ -46,6 +47,7 @@ class CastWebContentsView {
             contentView.requestFocus();
             contentViewRenderView.setCurrentWebContents(webContents);
             return () -> {
+                layout.setForeground(new ColorDrawable(backgroundColor));
                 layout.removeView(contentView);
                 layout.removeView(contentViewRenderView);
                 contentViewRenderView.destroy();