MacViews: Implemented Drag & Drop

ui/views/view.cc

 // Copyright (c) 2012 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.
 
 #define _USE_MATH_DEFINES // For VC++ to get M_PI. This has to be first.
 
 #include "ui/views/view.h"
 
 #include <algorithm>
 #include <cmath>
@@ skipping 2394 matching lines @@
 
   // Don't attempt to start a drag while in the process of dragging. This is
   // especially important on X where we can get multiple mouse move events when
   // we start the drag.
   if (widget->dragged_view())
     return false;
 
   OSExchangeData data;
   WriteDragData(press_pt, &data);
 
+#if defined(OS_MACOSX)
+  data.provider().SetNativeEvent(event.native_event());

[tapted, 2016/05/11 12:36:15]

This looks funny, but might be justified. It would be nice to isolate this in a
mac-specific file, or remove the #ifdef. Another way to do this might be to pass
the event in to a (maybe overloaded) constructor for OSExchangeData and just
ignore the argument on other platforms. Or perhaps pass the event into
Widget::RunShellDrag. However, I think there are other callers of RunShellDrag
that concoct their own OSExchangeData, and those other call sites might need to
work on Mac,  but we can't rely on callers remembering to do SetNativeEvent on
Mac.

Yet another cheaty way might be to simply use [NSApp currentEvent] inside
RunShellDrag. But that could be tricky to use in tests.

If it justified like this, we will need a good comment here to appease OWNERS
:). (along the lines of "On Mac, we Mac need to retain the native event here so
it can later be passed to .. etc.)

[spqchan, 2016/05/23 21:26:21]

I tried out the ideas you suggested but I think the simplest and cleanest way is
to just set it here.
I added a comment to explain it. Let me know though if you have other
suggestions!

+#endif
+
   // Message the RootView to do the drag and drop. That way if we're removed
   // the RootView can detect it and avoid calling us back.
   gfx::Point widget_location(event.location());
   ConvertPointToWidget(this, &widget_location);
   widget->RunShellDrag(this, data, widget_location, drag_operations, source);
   // WARNING: we may have been deleted.
   return true;
 }
 
 }  // namespace views