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

ui/views/widget/native_widget_aura.cc

 // 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.
 
 #include "ui/views/widget/native_widget_aura.h"
 
 #include "base/bind.h"
 #include "base/string_util.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/drag_drop_client.h"
@@ skipping 640 matching lines @@
   tooltip_manager_.reset();
   delegate_->OnNativeWidgetDestroyed();
   if (ownership_ == Widget::InitParams::NATIVE_WIDGET_OWNS_WIDGET)
     delete this;
 }
 
 void NativeWidgetAura::OnWindowVisibilityChanged(bool visible) {
   delegate_->OnNativeWidgetVisibilityChanged(visible);
 }
 
-bool NativeWidgetAura::CanDrop(const aura::DropTargetEvent& event) {
-  DCHECK(drop_helper_.get() != NULL);
-  View* view = drop_helper_->target_view();
-  if (view)
-    return view->CanDrop(event.data());
-  return false;
-}
-
 void NativeWidgetAura::OnDragEntered(const aura::DropTargetEvent& event) {
   DCHECK(drop_helper_.get() != NULL);
   drop_helper_->OnDragOver(event.data(), event.location(),
       event.source_operations());
 }
 
 int NativeWidgetAura::OnDragUpdated(const aura::DropTargetEvent& event) {
   DCHECK(drop_helper_.get() != NULL);
   return drop_helper_->OnDragOver(event.data(), event.location(),
       event.source_operations());
@@ skipping 96 matching lines @@
   NOTIMPLEMENTED();
 }
 
 // static
 bool NativeWidgetPrivate::IsMouseButtonDown() {
   return aura::Desktop::GetInstance()->IsMouseButtonDown();
 }
 
 }  // namespace internal
 }  // namespace views