fix a deadlock when removing a DisplayEventConnection

the deadlock would happen when the pipe became invalid and SF
trying to remove the connection from its list.

we know make sure to process events without holding a lock.

Change-Id: I39927ed8824fc7811e16db3c7608a2ebc72d9642
diff --git a/services/surfaceflinger/EventThread.h b/services/surfaceflinger/EventThread.h
index 0482ab7..4872c2b 100644
--- a/services/surfaceflinger/EventThread.h
+++ b/services/surfaceflinger/EventThread.h
@@ -58,6 +58,9 @@
     virtual status_t    readyToRun();
     virtual void        onFirstRef();
 
+    status_t removeDisplayEventConnection(
+            const wp<DisplayEventConnection>& connection);
+
     // constants
     sp<SurfaceFlinger> mFlinger;
     const DisplayHardware& mHw;