arc: add test for blocking incognito windows in screenshot

BUG=778852
TEST=ArcVoiceInteractionFrameworkServiceUnittest.
  CapturingScreenshotBlocksIncognitoWindows

Change-Id: I0bfa5a486759783d7c8926a309c6b5da9b02dcc6
Reviewed-on: https://chromium-review.googlesource.com/914983
Commit-Queue: Muyuan Li <muyuanli@chromium.org>
Reviewed-by: Luis Hector Chavez <lhchavez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536438}
  void OnClientConnectionLost() {
    client_.reset();
    binding_.Close();
  }

  void OnClientConnectionLost() {
    client_.reset();
    binding_.Close();
  }
