Adjust maximum scroll bounds on FrameView to account for top controls. (Blink-side)

public/web/WebWidget.h

Index: public/web/WebWidget.h
diff --git a/public/web/WebWidget.h b/public/web/WebWidget.h
index b8cd27940a6b0bc31cf3176454b10d2ad273501e..5342bb85d51a48b1983748acfeb26b06ba6c7ca1 100644
--- a/public/web/WebWidget.h
+++ b/public/web/WebWidget.h
@@ -261,6 +261,9 @@ public:
     // content.
     virtual WebColor backgroundColor() const { return 0xFFFFFFFF; /* SK_ColorWHITE */ }
 
+    // Sets the height subtracted from the Widget to accomodate the top controls.
+    virtual void setTopControlsLayoutHeight(float) { }
+
 protected:
     ~WebWidget() { }
 };