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

chrome/browser/cocoa/web_drag_source.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>
 
 #include "base/scoped_nsobject.h"
 #include "base/scoped_ptr.h"
 
 struct WebDropData;
 @class TabContentsViewCocoa;
 
 // A class that handles tracking and event processing for a drag and drop
 // originating from the content area.
 @interface WebDragSource : NSObject {
  @private
   // Our tab. Weak reference (owns or co-owns us).
   TabContentsViewCocoa* contentsView_;
 
   // Our drop data. Should only be initialized once.
   scoped_ptr<WebDropData> dropData_;
 
   // Our pasteboard.
   scoped_nsobject<NSPasteboard> pasteboard_;
+
+  // A mask of the allowed drag operations.
+  NSDragOperation dragOperationMask_;
 }
 
 // Initialize a WebDragSource object for a drag (originating on the given
 // contentsView and with the given dropData and pboard). Fill the pasteboard
 // with data types appropriate for dropData.
 - (id)initWithContentsView:(TabContentsViewCocoa*)contentsView
                   dropData:(const WebDropData*)dropData
-                pasteboard:(NSPasteboard*)pboard;
+                pasteboard:(NSPasteboard*)pboard
+         dragOperationMask:(NSDragOperation)dragOperationMask;
+
+// Returns a mask of the allowed drag operations.
+- (NSDragOperation)draggingSourceOperationMaskForLocal:(BOOL)isLocal;
 
 // Call when asked to do a lazy write to the pasteboard; hook up to
 // -pasteboard:provideDataForType: (on the contentsView).
 - (void)lazyWriteToPasteboard:(NSPasteboard*)pboard
                       forType:(NSString*)type;
 
 // Start the drag (on the originally provided contentsView); can do this right
 // after -initWithContentsView:....
 - (void)startDrag;
 
 // End the drag and clear the pasteboard; hook up to
 // -draggedImage:endedAt:operation:.
 - (void)endDragAt:(NSPoint)screenPoint
-      isCancelled:(BOOL)cancelled;
+        operation:(NSDragOperation)operation;
 
 // Drag moved; hook up to -draggedImage:movedTo:.
 - (void)moveDragTo:(NSPoint)screenPoint;
 
 // Call to drag a promised file to the given path (should be called before
 // -endDragAt:...); hook up to -namesOfPromisedFilesDroppedAtDestination:.
 // Returns the file name (not including path) of the file deposited (or which
 // will be deposited).
 - (NSString*)dragPromisedFileTo:(NSString*)path;
 
 @end