Improve watchdog monitor for InputReader and InputDispatcher.

Try harder to test for liveness.  There are situations where
the lock might not be held but the input system is stuck in
a callback into the window manager policy that has hung.

Bug: 5094994
Change-Id: Iff88655512a5dc8bbb4615be65f4115e975c020b
diff --git a/services/input/InputReader.h b/services/input/InputReader.h
index a122c97..ad89a22 100644
--- a/services/input/InputReader.h
+++ b/services/input/InputReader.h
@@ -363,6 +363,8 @@
 private:
     Mutex mLock;
 
+    Condition mReaderIsAliveCondition;
+
     sp<EventHubInterface> mEventHub;
     sp<InputReaderPolicyInterface> mPolicy;
     sp<QueuedInputListener> mQueuedListener;