OpenGL tracing.

Enable with:

adb shell setprop debug.egl.trace 1

Change-Id: Icfbc795f5260141510975228e72234e9aab56a85
diff --git a/opengl/libs/hooks.h b/opengl/libs/hooks.h
index 1ab58cc..812e26d 100644
--- a/opengl/libs/hooks.h
+++ b/opengl/libs/hooks.h
@@ -141,6 +141,11 @@
 
 #endif
 
+#if EGL_TRACE
+
+extern gl_hooks_t const* getGLTraceThreadSpecific();
+
+#endif
 
 // ----------------------------------------------------------------------------
 }; // namespace android