libgui: move fence handling into ConsumerBase

This change moves some common fence handling code into the base class for
BufferQueue consumer classes.  It also makes the ConsumerBase class initialize
a buffer slot's fence with the acquire fence every time a buffer is acquired.

Change-Id: I0bd88bc269e919653b659bfb3ebfb04dd61692a0
diff --git a/include/gui/SurfaceTexture.h b/include/gui/SurfaceTexture.h
index 2570cd9..80a010b 100644
--- a/include/gui/SurfaceTexture.h
+++ b/include/gui/SurfaceTexture.h
@@ -220,7 +220,7 @@
     // releaseBufferLocked overrides the ConsumerBase method to update the
     // mEglSlots array in addition to the ConsumerBase.
     virtual status_t releaseBufferLocked(int buf, EGLDisplay display,
-           EGLSyncKHR eglFence, const sp<Fence>& fence);
+           EGLSyncKHR eglFence);
 
     static bool isExternalFormat(uint32_t format);