mac: Don't lose pixels when copying a retina image from the clipboard.

ui/base/clipboard/clipboard_mac.h

 // Copyright 2014 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.
 
 #ifndef UI_BASE_CLIPBOARD_CLIPBOARD_MAC_H_
 #define UI_BASE_CLIPBOARD_CLIPBOARD_MAC_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "ui/base/clipboard/clipboard.h"
+#include "ui/base/ui_base_export.h"
 
 @class NSPasteboard;
 
 namespace ui {
 
-class ClipboardMac : public Clipboard {
+class UI_BASE_EXPORT ClipboardMac : public Clipboard {
  private:
   FRIEND_TEST_ALL_PREFIXES(ClipboardMacTest, ReadImageRetina);
   FRIEND_TEST_ALL_PREFIXES(ClipboardMacTest, ReadImageNonRetina);
   friend class Clipboard;
 
   ClipboardMac();
   ~ClipboardMac() override;
 
   // Clipboard overrides:
   uint64_t GetSequenceNumber(ClipboardType type) const override;
@@ skipping 34 matching lines @@
   void WriteData(const FormatType& format,
                  const char* data_data,
                  size_t data_len) override;
 
   DISALLOW_COPY_AND_ASSIGN(ClipboardMac);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_CLIPBOARD_CLIPBOARD_MAC_H_