Use const ref for LocalFrame::LocalFrameRoot and FrameTree::Top

third_party/WebKit/Source/core/page/DragController.cpp

 /*
  * Copyright (C) 2007, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 536 matching lines @@
     if (file_input->GetLayoutObject())
       DCHECK_EQ(file_input, element);
     if (file_input->IsDisabledFormControl())
       return false;
 
     return file_input->ReceiveDroppedFiles(drag_data);
   }
 
   // TODO(paulmeyer): Isn't |m_page->dragController()| the same as |this|?
   if (!page_->GetDragController().CanProcessDrag(
-          drag_data, *inner_frame->LocalFrameRoot())) {
+          drag_data, inner_frame->LocalFrameRoot())) {
     page_->GetDragCaret().Clear();
     return false;
   }
 
   if (page_->GetDragCaret().HasCaret()) {
     // TODO(editing-dev): Use of updateStyleAndLayoutIgnorePendingStylesheets
     // needs to be audited.  See http://crbug.com/590369 for more details.
     page_->GetDragCaret()
         .CaretPosition()
         .GetPosition()
@@ skipping 637 matching lines @@
 // TODO(esprehn): forLink is dead code, what was it for?
 void DragController::DoSystemDrag(DragImage* image,
                                   const IntPoint& drag_location,
                                   const IntPoint& event_pos,
                                   DataTransfer* data_transfer,
                                   LocalFrame* frame,
                                   bool for_link) {
   did_initiate_drag_ = true;
   drag_initiator_ = frame->GetDocument();
 
-  LocalFrame* main_frame = frame->LocalFrameRoot();
-  FrameView* main_frame_view = main_frame->View();
+  FrameView* main_frame_view = frame->LocalFrameRoot().View();
   IntPoint adjusted_drag_location = main_frame_view->RootFrameToContents(
       frame->View()->ContentsToRootFrame(drag_location));
   IntPoint adjusted_event_pos = main_frame_view->RootFrameToContents(
       frame->View()->ContentsToRootFrame(event_pos));
   WebDragData drag_data = data_transfer->GetDataObject()->ToWebDragData();
   WebDragOperationsMask drag_operation_mask =
       static_cast<WebDragOperationsMask>(data_transfer->SourceOperation());
   IntSize offset_size(adjusted_event_pos - adjusted_drag_location);
   WebPoint offset_point(offset_size.Width(), offset_size.Height());
   WebImage drag_image;
@@ skipping 42 matching lines @@
 
 DEFINE_TRACE(DragController) {
   visitor->Trace(page_);
   visitor->Trace(document_under_mouse_);
   visitor->Trace(drag_initiator_);
   visitor->Trace(drag_state_);
   visitor->Trace(file_input_element_under_mouse_);
 }
 
 }  // namespace blink