Allow ~Layer() to happen after onGLContextDestroyed

Bug: 19146354
Change-Id: I9e885936168bd541bfbed4064ad67ab524f58e32
diff --git a/libs/hwui/Layer.h b/libs/hwui/Layer.h
index 64d1d12..e196cb1 100644
--- a/libs/hwui/Layer.h
+++ b/libs/hwui/Layer.h
@@ -286,6 +286,12 @@
     void postDecStrong();
 
     /**
+     * Lost the GL context but the layer is still around, mark it invalid internally
+     * so the dtor knows not to do any GL work
+     */
+    void onGlContextLost();
+
+    /**
      * Bounds of the layer.
      */
     Rect layer;