Use eventfd instead of pipe in Looper.

Bug: 19933224
Change-Id: I6611e918db960bbb0e74f8308e10bdf79510b899
diff --git a/include/utils/Looper.h b/include/utils/Looper.h
index a381251..da2d5f2 100644
--- a/include/utils/Looper.h
+++ b/include/utils/Looper.h
@@ -447,8 +447,7 @@
 
     const bool mAllowNonCallbacks; // immutable
 
-    int mWakeReadPipeFd;  // immutable
-    int mWakeWritePipeFd; // immutable
+    int mWakeEventFd;  // immutable
     Mutex mLock;
 
     Vector<MessageEnvelope> mMessageEnvelopes; // guarded by mLock