Modify Webview drop effects.

Modify Webview drop effect override values.

Used for gears file drag & drop in chrome, define the values of
the drop effect overrides to match the gears definitions.

BUG=7995

[noel.gordon_gmail.com, 2009-04-30 17:57:25]

So if gears needs to support new drop effects in future, we just add new values
to the end of the chrome webview_imlp.h enum.  For reference, the gears
code-base currently defines the drop effects as follows:

enum DragAndDropCursorType {
  DRAG_AND_DROP_CURSOR_NONE,
  DRAG_AND_DROP_CURSOR_COPY
};

[tony, 2009-04-30 18:19:16]

LGTM.  I'll land later today.

[noel.gordon_gmail.com, 2009-04-30 19:23:50]

Thanks!

[tony, 2009-04-30 19:30:50]

Landed in r14971