Add setNeedsLayoutAndFullPaintInvalidation to WebWidget.

public/web/WebWidget.h

Index: public/web/WebWidget.h
diff --git a/public/web/WebWidget.h b/public/web/WebWidget.h
index ddd8a4e05d4b1775283b2213eaa3e5c7872ade25..741396430cbdd55bc269fe916baaebc1ecc40432 100644
--- a/public/web/WebWidget.h
+++ b/public/web/WebWidget.h
@@ -92,6 +92,10 @@ public:
     // paint, although the client can rate-limit these calls.
     virtual void beginFrame(const WebBeginFrameArgs& frameTime) { }
 
+    // Called when the Widget contents has changed in such a way the layout must be
+    // redone, and any resulting paint invalidations issued.
+    virtual void setNeedsLayoutAndFullPaintInvalidation() { }
+
     // Called to layout the WebWidget. This MUST be called before Paint,
     // and it may result in calls to WebWidgetClient::didInvalidateRect.
     virtual void layout() { }