Plumb the DragOperation through all the layers between the platform DnD code ...

chrome/browser/cocoa/web_drop_target.h

 // Copyright (c) 2009 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 <Cocoa/Cocoa.h>
 
 class RenderViewHost;
 class TabContents;
 class WebDropData;
 
 // A typedef for a RenderViewHost used for comparison purposes only.
 typedef RenderViewHost* RenderViewHostIdentifier;
 
 // A class that handles tracking and event processing for a drag and drop
 // over the content area. Assumes something else initiates the drag, this is
 // only for processing during a drag.
 
 @interface WebDropTarget : NSObject {
  @private
   // Our associated TabContents. Weak reference.
   TabContents* tabContents_;
 
   // Updated asynchronously during a drag to tell us whether or not we should
   // allow the drop.
-  BOOL isDropTarget_;
+  NSDragOperation current_operation_;
 
   // Keep track of the render view host we're dragging over.  If it changes
   // during a drag, we need to re-send the DragEnter message.
   RenderViewHostIdentifier currentRVH_;
 }
 
 // |contents| is the TabContents representing this tab, used to communicate
 // drag&drop messages to WebCore and handle navigation on a successful drop
 // (if necessary).
 - (id)initWithTabContents:(TabContents*)contents;
 
-// Call to set whether or not we should allow the drop. Takes effect the
+// Sets the current operation negotiated by the source and destination,
+// which determines whether or not we should allow the drop. Takes effect the
 // next time |-draggingUpdated:| is called.
-- (void)setIsDropTarget:(BOOL)isDropTarget;
+- (void)setCurrentOperation: (NSDragOperation)operation;
 
 // Messages to send during the tracking of a drag, ususally upon receiving
 // calls from the view system. Communicates the drag messages to WebCore.
 - (NSDragOperation)draggingEntered:(id<NSDraggingInfo>)info
                               view:(NSView*)view;
 - (void)draggingExited:(id<NSDraggingInfo>)info;
 - (NSDragOperation)draggingUpdated:(id<NSDraggingInfo>)info
                               view:(NSView*)view;
 - (BOOL)performDragOperation:(id<NSDraggingInfo>)info
                               view:(NSView*)view;
@@ skipping 13 matching lines @@
              fromPasteboard:(NSPasteboard*)pboard;
 // Given a point in window coordinates and a view in that window, return a
 // flipped point in the coordinate system of |view|.
 - (NSPoint)flipWindowPointToView:(const NSPoint&)windowPoint
                             view:(NSView*)view;
 // Given a point in window coordinates and a view in that window, return a
 // flipped point in screen coordinates.
 - (NSPoint)flipWindowPointToScreen:(const NSPoint&)windowPoint
                               view:(NSView*)view;
 @end