EGL: add GPU frame completion tracing

This change adds a debug option to EGL to use an EGLSyncKHR each frame to
determine when the GPU finishes rendering the frame.

Change-Id: I09ce071db904b44f07ca814c586c291c8b59385a
diff --git a/opengl/libs/EGL/egl_display.h b/opengl/libs/EGL/egl_display.h
index 43738ea..3e22efa 100644
--- a/opengl/libs/EGL/egl_display.h
+++ b/opengl/libs/EGL/egl_display.h
@@ -107,7 +107,8 @@
 
 public:
     DisplayImpl     disp;
-    bool    finishOnSwap;
+    bool    finishOnSwap;       // property: debug.egl.finish
+    bool    traceGpuCompletion; // property: debug.egl.traceGpuCompletion
 
 private:
             uint32_t                    refs;