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

public/web/WebView.h

Index: public/web/WebView.h
diff --git a/public/web/WebView.h b/public/web/WebView.h
index da572e02dc5e352e277949e25755ebc73be4033f..24e3557c9a27be1eaf6e129e68831b48ab76ae00 100644
--- a/public/web/WebView.h
+++ b/public/web/WebView.h
@@ -493,6 +493,10 @@ public:
 
     // Testing functionality for TestRunner ---------------------------------
 
+    // Force the webgl context to fail so that webglcontextcreationerror
+    // event gets generated/tested.
+    virtual void forceNextWebGLContextCreationToFail() = 0;
+
 protected:
     ~WebView() {}
 };