Allow dragging a download only after the download is complete.

chrome/browser/ui/cocoa/download/download_util_mac.mm

 // Copyright (c) 2011 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.
 //
 // Download utility implementation for Mac OS X.
 
 #include "chrome/browser/ui/cocoa/download/download_util_mac.h"
 
+#include "base/logging.h"
 #include "base/sys_string_conversions.h"
 #include "content/public/browser/download_item.h"
 #include "content/public/browser/download_manager.h"
 #include "ui/gfx/image/image.h"
 #include "ui/gfx/native_widget_types.h"
 
 using content::DownloadItem;
 
 namespace download_util {
 
 void AddFileToPasteboard(NSPasteboard* pasteboard, const FilePath& path) {
   // Write information about the file being dragged to the pasteboard.
   NSString* file = base::SysUTF8ToNSString(path.value());
   NSArray* fileList = [NSArray arrayWithObject:file];
   [pasteboard declareTypes:[NSArray arrayWithObject:NSFilenamesPboardType]
                      owner:nil];
   [pasteboard setPropertyList:fileList forType:NSFilenamesPboardType];
 }
 
 void DragDownload(const DownloadItem* download,
                   gfx::Image* icon,
                   gfx::NativeView view) {
+  DCHECK(download->IsComplete());
   NSPasteboard* pasteboard = [NSPasteboard pasteboardWithName:NSDragPboard];
-  AddFileToPasteboard(pasteboard, download->GetFullPath());
+  AddFileToPasteboard(pasteboard, download->GetTargetFilePath());
 
   // Synthesize a drag event, since we don't have access to the actual event
   // that initiated a drag (possibly consumed by the Web UI, for example).
   NSPoint position = [[view window] mouseLocationOutsideOfEventStream];
   NSTimeInterval eventTime = [[NSApp currentEvent] timestamp];
   NSEvent* dragEvent = [NSEvent mouseEventWithType:NSLeftMouseDragged
                                           location:position
                                      modifierFlags:NSLeftMouseDraggedMask
                                          timestamp:eventTime
                                       windowNumber:[[view window] windowNumber]
                                            context:nil
                                        eventNumber:0
                                         clickCount:1
                                           pressure:1.0];
 
   // Run the drag operation.
   [[view window] dragImage:icon->ToNSImage()
                         at:position
                     offset:NSZeroSize
                      event:dragEvent
                 pasteboard:pasteboard
                     source:view
                  slideBack:YES];
 }
 
 }  // namespace download_util