[WebGL-blink] Add test function to force fail the webgl-context

public/web/WebWidget.h

Index: public/web/WebWidget.h
diff --git a/public/web/WebWidget.h b/public/web/WebWidget.h
index d191c26e509affb2483959ea816c4429e4b67782..ce99b6afc08d9cfb6b8db852772fb5cae508932b 100644
--- a/public/web/WebWidget.h
+++ b/public/web/WebWidget.h
@@ -273,6 +273,8 @@ public:
     // Sets the height subtracted from the Widget to accomodate the top controls.
     virtual void setTopControlsLayoutHeight(float) { }
 
+    virtual void forceNextWebGLContextCreationToFail(bool forceFailContext) { }
+
 protected:
     ~WebWidget() { }
 };