Make drag and drop work on webpage. Also slightly modify drag drop workflow.

ui/views/widget/native_widget_aura.h

 // 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.
 
 #ifndef UI_VIEWS_WIDGET_NATIVE_WIDGET_AURA_H_
 #define UI_VIEWS_WIDGET_NATIVE_WIDGET_AURA_H_
 #pragma once
 
 #include "base/memory/scoped_vector.h"
 #include "base/memory/weak_ptr.h"
@@ skipping 123 matching lines @@
   virtual bool ShouldActivate(aura::Event* event) OVERRIDE;
   virtual void OnActivated() OVERRIDE;
   virtual void OnLostActive() OVERRIDE;
   virtual void OnCaptureLost() OVERRIDE;
   virtual void OnPaint(gfx::Canvas* canvas) OVERRIDE;
   virtual void OnWindowDestroying() OVERRIDE;
   virtual void OnWindowDestroyed() OVERRIDE;
   virtual void OnWindowVisibilityChanged(bool visible) OVERRIDE;
 
   // Overridden from aura::WindowDragDropDelegate:
-  virtual bool CanDrop(const aura::DropTargetEvent& event) OVERRIDE;
   virtual void OnDragEntered(const aura::DropTargetEvent& event) OVERRIDE;
   virtual int OnDragUpdated(const aura::DropTargetEvent& event) OVERRIDE;
   virtual void OnDragExited() OVERRIDE;
   virtual int OnPerformDrop(const aura::DropTargetEvent& event) OVERRIDE;
 
  protected:
   internal::NativeWidgetDelegate* delegate() { return delegate_; }
 
  private:
   class DesktopObserverImpl;
@@ skipping 19 matching lines @@
   scoped_ptr<DesktopObserverImpl> desktop_observer_;
 
   scoped_ptr<DropHelper> drop_helper_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeWidgetAura);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_NATIVE_WIDGET_AURA_H_