aura: Add flag to indicate if a drag session is started with touch or mouse.

ui/views/widget/widget.cc

Index: ui/views/widget/widget.cc
diff --git a/ui/views/widget/widget.cc b/ui/views/widget/widget.cc
index 41752a52a98e75caf7bfbccd32030d6b24dc6e0d..e3f2ddf34ecd07a7e89b13b91ca74e569a36a2ba 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -708,9 +708,10 @@ InputMethod* Widget::GetInputMethod() {
 void Widget::RunShellDrag(View* view,
                           const ui::OSExchangeData& data,
                           const gfx::Point& location,
-                          int operation) {
+                          int operation,
+                          ui::DragDropTypes::DragEventSource source) {
   dragged_view_ = view;
-  native_widget_->RunShellDrag(view, data, location, operation);
+  native_widget_->RunShellDrag(view, data, location, operation, source);
   // If the view is removed during the drag operation, dragged_view_ is set to
   // NULL.
   if (view && dragged_view_ == view) {