DO NOT MERGE Revert "MediaRouterButton: Make the button always enabled"

This reverts commit 8a54ce6b8b595c145ea534510d5d1904ee7d5415.

Bug: 32108506
Change-Id: I6ad89c7df0f1991d45696f33efb8b0b1bbe67bcc
(cherry picked from commit 44f505b3340199ca7f31f0912bd6de227ab36899)
diff --git a/v7/mediarouter/src/android/support/v7/app/MediaRouteButton.java b/v7/mediarouter/src/android/support/v7/app/MediaRouteButton.java
index 20e83aa..25288c0 100644
--- a/v7/mediarouter/src/android/support/v7/app/MediaRouteButton.java
+++ b/v7/mediarouter/src/android/support/v7/app/MediaRouteButton.java
@@ -513,6 +513,9 @@
                     }
                 }
             }
+
+            setEnabled(mRouter.isRouteAvailable(mSelector,
+                    MediaRouter.AVAILABILITY_FLAG_IGNORE_DEFAULT_ROUTE));
         }
     }