[Presentation API, Android] Enable MediaRouter for Android

Remove the #enable-media-router flag from chrome://flags.
Always return true for Android.

BUG=524131

Review URL: https://codereview.chromium.org/1392883003

Cr-Commit-Position: refs/heads/master@{#353104}
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index 63237e4..760dfe0 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -1877,13 +1877,13 @@
      kOsDesktop,
      ENABLE_DISABLE_VALUE_TYPE(switches::kV8PacMojoOutOfProcess,
                                switches::kDisableOutOfProcessPac)},
-#if defined(ENABLE_MEDIA_ROUTER)
+#if defined(ENABLE_MEDIA_ROUTER) && !defined(OS_ANDROID)
     {"enable-media-router",
      IDS_FLAGS_ENABLE_MEDIA_ROUTER_NAME,
      IDS_FLAGS_ENABLE_MEDIA_ROUTER_DESCRIPTION,
-     kOsAll,
+     kOsDesktop,
      SINGLE_VALUE_TYPE(switches::kEnableMediaRouter)},
-#endif  // defined(ENABLE_MEDIA_ROUTER)
+#endif  // defined(ENABLE_MEDIA_ROUTER) && !defined(OS_ANDROID)
 // Since Drive Search is not available when app list is disabled, flag guard
 // enable-drive-search-in-chrome-launcher flag.
 #if defined(ENABLE_APP_LIST)