Not create CastRemotingConnector if MediaRouter is disabled.

CastRemotingConnector depends on MediaRouter, which should not be
created when MediaRouter is disabled by an admin policy.

Bug: 836042
Change-Id: Ibd03b5f7c0cb875173cb8c6c573f34a12f0e22b4
Reviewed-on: https://chromium-review.googlesource.com/1026252Reviewed-by: Adam Parker <amp@chromium.org>
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Commit-Queue: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553932}

chrome/browser/media/cast_remoting_connector.cc

@@ -15,6 +15,7 @@
 #include "build/build_config.h"
 #include "chrome/browser/media/router/media_router.h"
 #include "chrome/browser/media/router/media_router_factory.h"
+#include "chrome/browser/media/router/media_router_feature.h"
 #include "chrome/browser/sessions/session_tab_helper.h"
 #include "chrome/common/chrome_features.h"
 #include "components/mirroring/browser/cast_remoting_sender.h"
@@ -132,6 +133,8 @@ CastRemotingConnector* CastRemotingConnector::Get(
     const SessionID tab_id = SessionTabHelper::IdForTab(contents);
     if (!tab_id.is_valid())
       return nullptr;
+    if (!media_router::MediaRouterEnabled(contents->GetBrowserContext()))
+      return nullptr;
     connector = new CastRemotingConnector(
         media_router::MediaRouterFactory::GetApiForBrowserContext(
             contents->GetBrowserContext()),