Make CastWebContentsService foreground when playing audio.

When the CastWebContentsService plays audio, we need to make it a
foreground service so the sandbox process doesn't get killed by the OOM
killer.

Bug: 68138999
Test: manual test on device: sandboxed process isn't cached when we
casting

Change-Id: Ief340684ca77fada6badb580922b97fffa1cdb55
Reviewed-on: https://chromium-review.googlesource.com/738621
Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Ralph Nathan <ralphnathan@google.com>
Cr-Commit-Position: refs/heads/master@{#511743}

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

@@ -4,6 +4,7 @@
 
 package org.chromium.chromecast.shell;
 
+import android.app.Notification;
 import android.app.Service;
 import android.content.Intent;
 import android.media.AudioManager;
@@ -28,6 +29,7 @@
 public class CastWebContentsService extends Service {
     private static final String TAG = "cr_CastWebService";
     private static final boolean DEBUG = true;
+    private static final int CAST_NOTIFICATION_ID = 100;
 
     private String mInstanceId;
     private AudioManager mAudioManager;
@@ -94,6 +96,9 @@ public IBinder onBind(Intent intent) {
     private void showWebContents(WebContents webContents) {
         if (DEBUG) Log.d(TAG, "showWebContents");
 
+        Notification notification = new Notification.Builder(this).build();
+        startForeground(CAST_NOTIFICATION_ID, notification);
+
         // TODO(derekjchow): productVersion
         mContentViewCore = new ContentViewCore(this, "");
         mContentView = ContentView.createContentView(this, mContentViewCore);
@@ -106,6 +111,9 @@ private void showWebContents(WebContents webContents) {
     // Remove the currently displayed webContents. no-op if nothing is being displayed.
     private void detachWebContentsIfAny() {
         if (DEBUG) Log.d(TAG, "detachWebContentsIfAny");
+
+        stopForeground(true /*removeNotification*/ );
+
         if (mContentView != null) {
             mContentView = null;
             mContentViewCore = null;