Cancel drag operation when the tab RenderWidgetHostView does not exist (Mac)

content/browser/renderer_host/render_widget_host_input_event_router.h

Index: content/browser/renderer_host/render_widget_host_input_event_router.h
diff --git a/content/browser/renderer_host/render_widget_host_input_event_router.h b/content/browser/renderer_host/render_widget_host_input_event_router.h
index e74b3a82d3b5aad53efa2772a2fc22e68a2f5c2b..721ccffa0fa6d22dc9bf234de61a5c0f9dbf68e9 100644
--- a/content/browser/renderer_host/render_widget_host_input_event_router.h
+++ b/content/browser/renderer_host/render_widget_host_input_event_router.h
@@ -86,7 +86,8 @@ class CONTENT_EXPORT RenderWidgetHostInputEventRouter
   // Returns the RenderWidgetHostImpl inside the |root_view| at |point| where
   // |point| is with respect to |root_view|'s coordinates. If a RWHI is found,
   // the value of |transformed_point| is the coordinate of the point with
-  // respect to the RWHI's coordinates.
+  // respect to the RWHI's coordinates. If |root_view| is nullptr, this method
+  // will return nullptr and will not modify |transformed_point|.
   RenderWidgetHostImpl* GetRenderWidgetHostAtPoint(
       RenderWidgetHostViewBase* root_view,
       const gfx::Point& point,