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

content/browser/renderer_host/render_widget_host_input_event_router.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_INPUT_EVENT_ROUTER_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_INPUT_EVENT_ROUTER_H_
 
 #include <stdint.h>
 
 #include <deque>
@@ skipping 68 matching lines @@
 
   bool is_registered(const cc::FrameSinkId& id) {
     return owner_map_.find(id) != owner_map_.end();
   }
 
   void OnHittestData(const FrameHostMsg_HittestData_Params& params);
 
   // 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,
       gfx::Point* transformed_point);
 
  private:
   struct HittestData {
     bool ignored_for_hittest;
   };
 
@@ skipping 78 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostInputEventRouter);
   FRIEND_TEST_ALL_PREFIXES(SitePerProcessBrowserTest,
                            InputEventRouterGestureTargetQueueTest);
   FRIEND_TEST_ALL_PREFIXES(SitePerProcessBrowserTest,
                            InputEventRouterTouchpadGestureTargetTest);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_INPUT_EVENT_ROUTER_H_