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

content/browser/web_contents/web_drag_dest_mac.mm

 // Copyright (c) 2012 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.
 
 #import "content/browser/web_contents/web_drag_dest_mac.h"
 
 #import <Carbon/Carbon.h>
 
 #include "base/strings/sys_string_conversions.h"
 #include "content/browser/renderer_host/render_view_host_impl.h"
@@ skipping 116 matching lines @@
   // Save off the RVH so we can tell if it changes during a drag. If it does,
   // we need to send a new enter message in draggingUpdated:.
   currentRVH_ = webContents_->GetRenderViewHost();
 
   // Create the appropriate mouse locations for WebCore. The draggingLocation
   // is in window coordinates. Both need to be flipped.
   NSPoint windowPoint = [info draggingLocation];
   NSPoint viewPoint = [self flipWindowPointToView:windowPoint view:view];
   NSPoint screenPoint = [self flipWindowPointToScreen:windowPoint view:view];
   gfx::Point transformedPt;
+  if (!webContents_->GetRenderWidgetHostView()) {
+    // This could happen when the renderer process for the top-level RWH crashes
+    // (see https://crbug.com/670645).
+    canceled_ = true;
+    return NSDragOperationNone;
+  }
   currentRWHForDrag_ =
       [self GetRenderWidgetHostAtPoint:viewPoint transformedPt:&transformedPt]
           ->GetWeakPtr();
 
   // Fill out a DropData from pasteboard.
   std::unique_ptr<DropData> dropData;
   dropData.reset(new DropData());
   [self populateDropData:dropData.get()
              fromPasteboard:[info draggingPasteboard]];
   // TODO(paulmeyer): Data may be pulled from the pasteboard multiple times per
@@ skipping 49 matching lines @@
 
   if (currentRWHForDrag_) {
     currentRWHForDrag_->DragTargetDragLeave();
     currentRWHForDrag_.reset();
   }
   dropData_.reset();
 }
 
 - (NSDragOperation)draggingUpdated:(id<NSDraggingInfo>)info
                               view:(NSView*)view {
+  if (canceled_)
+    return NSDragOperationNone;

[dcheng, 2016/12/03 00:33:07]

Seems unusual that this condition is checked twice in this function.

[EhsanK, 2016/12/03 00:36:44]

I think draggingEntered could also mutate |canceled_|.

[dcheng, 2016/12/03 00:49:14]

Right, I understand, that was there even before we rewrote this to support
OOPIF.

It just feels weird: canceled_ originally represented whether or not the
delegate cancelled the drag. Now it means that, and "there is no RWHV", and it
feels like the two checks are entangled in a slightly unusual way.

[EhsanK, 2016/12/03 00:59:37]

I see your point. I could instead not change canceled_ but at the top verify if
|RWHV| exists.

[dcheng, 2016/12/03 01:02:32]

Meh, I can't really think of anything better atm. We need to clean this code up
anyway (we double hit-test in the draggingUpdated but not draggingEntered yet
case), we can figure it out then =)

[EhsanK, 2016/12/03 01:13:50]

I added TODOs (on behalf of paulmeyer@ as well hope that is alright).  I could
also remove this cancel and repeat verifying GetRenderWidgetHostView() ==
nullptr like above. WDYT?

+
   // Create the appropriate mouse locations for WebCore. The draggingLocation
   // is in window coordinates. Both need to be flipped.
   NSPoint windowPoint = [info draggingLocation];
   NSPoint viewPoint = [self flipWindowPointToView:windowPoint view:view];
   NSPoint screenPoint = [self flipWindowPointToScreen:windowPoint view:view];
   gfx::Point transformedPt;
   content::RenderWidgetHostImpl* targetRWH =
       [self GetRenderWidgetHostAtPoint:viewPoint transformedPt:&transformedPt];
 
   // TODO(paulmeyer): The dragging delegates may now by invoked multiple times
@@ skipping 138 matching lines @@
   // Get custom MIME data.
   if ([types containsObject:ui::kWebCustomDataPboardType]) {
     NSData* customData = [pboard dataForType:ui::kWebCustomDataPboardType];
     ui::ReadCustomDataIntoMap([customData bytes],
                               [customData length],
                               &data->custom_data);
   }
 }
 
 @end