Call WebContentsDelegate::CanDragEnter from WebContentsViewAura.

content/browser/web_contents/web_contents_view_aura.cc

Index: content/browser/web_contents/web_contents_view_aura.cc
===================================================================
--- content/browser/web_contents/web_contents_view_aura.cc	(revision 263053)
+++ content/browser/web_contents/web_contents_view_aura.cc	(working copy)
@@ -1417,17 +1417,25 @@
 // WebContentsViewAura, aura::client::DragDropDelegate implementation:
 
 void WebContentsViewAura::OnDragEntered(const ui::DropTargetEvent& event) {
-  if (drag_dest_delegate_)
-    drag_dest_delegate_->DragInitialize(web_contents_);
-
+  current_rvh_for_drag_ = web_contents_->GetRenderViewHost();
   current_drop_data_.reset(new DropData());
 
   PrepareDropData(current_drop_data_.get(), event.data());
   blink::WebDragOperationsMask op = ConvertToWeb(event.source_operations());
 
+  // Give the delegate an opportunity to cancel the drag.
+  if (!web_contents_->GetDelegate()->CanDragEnter(web_contents_,
+                                                  *current_drop_data_.get(),
+                                                  op)) {
+    current_drop_data_.reset(NULL);
+    return;
+  }
+
+  if (drag_dest_delegate_)
+    drag_dest_delegate_->DragInitialize(web_contents_);
+
   gfx::Point screen_pt =
       gfx::Screen::GetScreenFor(GetNativeView())->GetCursorScreenPoint();
-  current_rvh_for_drag_ = web_contents_->GetRenderViewHost();
   web_contents_->GetRenderViewHost()->DragTargetDragEnter(
       *current_drop_data_.get(), event.location(), screen_pt, op,
       ConvertAuraEventFlagsToWebInputEventModifiers(event.flags()));
@@ -1443,6 +1451,9 @@
   if (current_rvh_for_drag_ != web_contents_->GetRenderViewHost())
     OnDragEntered(event);
 
+  if (!current_drop_data_)
+    return ui::DragDropTypes::DRAG_NONE;
+
   blink::WebDragOperationsMask op = ConvertToWeb(event.source_operations());
   gfx::Point screen_pt =
       gfx::Screen::GetScreenFor(GetNativeView())->GetCursorScreenPoint();
@@ -1461,6 +1472,9 @@
   if (current_rvh_for_drag_ != web_contents_->GetRenderViewHost())
     return;
 
+  if (!current_drop_data_)
+    return;
+
   web_contents_->GetRenderViewHost()->DragTargetDragLeave();
   if (drag_dest_delegate_)
     drag_dest_delegate_->OnDragLeave();
@@ -1473,6 +1487,9 @@
   if (current_rvh_for_drag_ != web_contents_->GetRenderViewHost())
     OnDragEntered(event);
 
+  if (!current_drop_data_)
+    return ui::DragDropTypes::DRAG_NONE;
+
   web_contents_->GetRenderViewHost()->DragTargetDrop(
       event.location(),
       gfx::Screen::GetScreenFor(GetNativeView())->GetCursorScreenPoint(),