[CRD iOS] Allow HostViewController to auto-hide the home indicator

This CL makes HostViewController request to autohide the home indicator
(the bar acting like a virtual home button), so that user can see
things on the bottom after the home indicator times out.

This CL is dependent on internal CL:
https://chrome-internal-review.googlesource.com/c/chrome/ios_internal/+/666568

Bug: 876014
Change-Id: I4d5e3f983100dd43f84f5d422bba31207707c651
Reviewed-on: https://chromium-review.googlesource.com/1187655
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585678}

remoting/ios/app/host_view_controller.mm

@@ -187,6 +187,12 @@ static NSString* const kFeedbackContext = @"InSessionFeedbackContext";
   return YES;
 }
 
+- (BOOL)prefersHomeIndicatorAutoHidden {
+  // Allow home indicator to timeout so that user can see desktop on the bottom
+  // of the screen.
+  return YES;
+}
+
 - (void)viewDidAppear:(BOOL)animated {
   [super viewDidAppear:animated];
   [_client.displayHandler createRendererContext:_hostView];