Implement Clipboard::ReadData and Clipboard::WriteData for Mac.

ui/base/clipboard/clipboard_win.cc

 // Copyright (c) 2011 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.
 
 // Many of these functions are based on those found in
 // webkit/port/platform/PasteboardWin.cpp
 
 #include "ui/base/clipboard/clipboard.h"
 
 #include <shlobj.h>
@@ skipping 602 matching lines @@
     for (int i = 0; i < count; ++i) {
       UINT size = ::DragQueryFile(drop, i, NULL, 0) + 1;
       DCHECK_GT(size, 1u);
       std::wstring file;
       ::DragQueryFile(drop, i, WriteInto(&file, size), size);
       files->push_back(FilePath(file));
     }
   }
 }
 
-void Clipboard::ReadData(const std::string& format, std::string* result) {
+void Clipboard::ReadData(const std::string& format, std::string* result) const {
   if (!result) {
     NOTREACHED();
     return;
   }
 
   CLIPFORMAT clip_format =
       ::RegisterClipboardFormat(ASCIIToWide(format).c_str());
 
   ScopedClipboard clipboard;
   if (!clipboard.Acquire(GetClipboardWindow()))
@@ skipping 111 matching lines @@
     clipboard_owner_ = ::CreateWindow(L"ClipboardOwnerWindowClass",
                                       L"ClipboardOwnerWindow",
                                       0, 0, 0, 0, 0,
                                       HWND_MESSAGE,
                                       0, 0, 0);
   }
   return clipboard_owner_;
 }
 
 }  // namespace ui