mac: Add tests for reading images from NSPasteboard.

ui/base/clipboard/clipboard_mac.h

Index: ui/base/clipboard/clipboard_mac.h
diff --git a/ui/base/clipboard/clipboard_mac.h b/ui/base/clipboard/clipboard_mac.h
index 3a4ef4a40e145f510d83baadeadf95d3910dfa30..2e264cb0171966e4891200c58d4b276dd01df703 100644
--- a/ui/base/clipboard/clipboard_mac.h
+++ b/ui/base/clipboard/clipboard_mac.h
@@ -8,13 +8,19 @@
 #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();
@@ -36,6 +42,7 @@ class ClipboardMac : public Clipboard {
                 uint32_t* fragment_start,
                 uint32_t* fragment_end) const override;
   void ReadRTF(ClipboardType type, std::string* result) const override;
+  SkBitmap ReadImage(ClipboardType type, NSPasteboard* pb) const;
   SkBitmap ReadImage(ClipboardType type) const override;
   void ReadCustomData(ClipboardType clipboard_type,
                       const base::string16& type,