Make RenderFrameHostImpl::GetRenderWidgetHost() always return an object

content/browser/frame_host/render_frame_host_impl.h

 // Copyright 2013 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_FRAME_HOST_RENDER_FRAME_HOST_IMPL_H_
 #define CONTENT_BROWSER_FRAME_HOST_RENDER_FRAME_HOST_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 234 matching lines @@
   // FrameTreeNode. The proper way to check whether a frame is loading is to
   // call FrameTreeNode::IsLoading.
   bool is_loading() const { return is_loading_; }
 
   // Sets this RenderFrameHost loading state. This is only used in the case of
   // transfer navigations, where no DidStart/DidStopLoading notifications
   // should be sent during the transfer.
   // TODO(clamy): Remove this once PlzNavigate ships.
   void set_is_loading(bool is_loading) { is_loading_ = is_loading; }
 
-  // This returns the RenderFrameHost's owned RenderWidgetHost if it has one,
-  // or else it returns nullptr.
-  // If the RenderFrameHost is the page's main frame, this returns instead a
-  // pointer to the RenderViewHost (which inherits RenderWidgetHost).
+  // Returns true if this is a top-level frame, or if this frame's RenderFrame
+  // is in a different process from its parent frame. Local roots are
+  // distinguished by owning a RenderWidgetHost, which manages input events
+  // and painting for this frame and its contiguous local subtree in the
+  // renderer process.
+  bool is_local_root() { return !!render_widget_host_; }
+
+  // Returns the RenderWidgetHostImpl attached to this frame or the nearest
+  // ancestor frame, which could potentially be the root. For most input
+  // and rendering related purposes, GetView() should be preferred and
+  // RenderWidgetHostViewBase methods used. GetRenderWidgetHost() will not
+  // return a nullptr, whereas GetView() potentially will (for instance,
+  // after a renderer crash).
+  //
+  // This method crashes if this RenderFrameHostImpl does not own a
+  // a RenderWidgetHost and nor does any of its ancestors. That would
+  // typically mean that the frame has been detached from the frame tree.
   RenderWidgetHostImpl* GetRenderWidgetHost();
 
   GlobalFrameRoutingId GetGlobalFrameRoutingId();
 
   // This function is called when this is a swapped out RenderFrameHost that
   // lives in the same process as the parent frame. The
   // |cross_process_frame_connector| allows the non-swapped-out
   // RenderFrameHost for a frame to communicate with the parent process
   // so that it may composite drawing data.
   //
@@ skipping 710 matching lines @@
 
   // NOTE: This must be the last member.
   base::WeakPtrFactory<RenderFrameHostImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderFrameHostImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_FRAME_HOST_RENDER_FRAME_HOST_IMPL_H_