Plumb event flags (shift/alt/ctrl modifiers) for drag/drop events to WebKit.

ash/drag_drop/drag_drop_controller.cc

Index: ash/drag_drop/drag_drop_controller.cc
diff --git a/ash/drag_drop/drag_drop_controller.cc b/ash/drag_drop/drag_drop_controller.cc
index 5a3f7df11af78d713f00ca394ac9db092a8542c5..1d5e3a12748ff038d05daadcb19c9e6b10d07c4f 100644
--- a/ash/drag_drop/drag_drop_controller.cc
+++ b/ash/drag_drop/drag_drop_controller.cc
@@ -104,6 +104,7 @@ void DragDropController::DragUpdate(aura::Window* target,
                               event.location(),
                               event.root_location(),
                               drag_operation_);
+      e.set_flags(event.flags());
       delegate->OnDragEntered(e);
     }
   } else {
@@ -112,6 +113,7 @@ void DragDropController::DragUpdate(aura::Window* target,
                               event.location(),
                               event.root_location(),
                               drag_operation_);
+      e.set_flags(event.flags());
       int op = delegate->OnDragUpdated(e);
       gfx::NativeCursor cursor = (op == ui::DragDropTypes::DRAG_NONE)?
           ui::kCursorMove : ui::kCursorHand;
@@ -138,6 +140,7 @@ void DragDropController::Drop(aura::Window* target,
   if ((delegate = aura::client::GetDragDropDelegate(target))) {
     aura::DropTargetEvent e(
         *drag_data_, event.location(), event.root_location(), drag_operation_);
+    e.set_flags(event.flags());
     drag_operation_ = delegate->OnPerformDrop(e);
     if (drag_operation_ == 0)
       StartCanceledAnimation();