Change Clipboard to use virtual methods for testing purposes.

ui/base/BUILD.gn

 # 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.
 
 import("//build/config/ui.gni")
 
 if (is_android) {
   import("//build/config/android/config.gni")
   import("//build/config/android/rules.gni")
 }
@@ skipping 19 matching lines @@
     "android/view_android.h",
     "android/window_android.cc",
     "android/window_android.h",
     "android/window_android_compositor.h",
     "android/window_android_observer.h",
     "base_window.cc",
     "base_window.h",
     "clipboard/clipboard.cc",
     "clipboard/clipboard.h",
     "clipboard/clipboard_android.cc",
-    "clipboard/clipboard_android_initialization.h",
+    "clipboard/clipboard_android.h",
     "clipboard/clipboard_constants.cc",
+    "clipboard/clipboard_mac.h",
     "clipboard/clipboard_mac.mm",
     "clipboard/clipboard_types.h",
     "clipboard/clipboard_util_win.cc",
     "clipboard/clipboard_util_win.h",
     "clipboard/clipboard_win.cc",
+    "clipboard/clipboard_win.h",
     "clipboard/custom_data_helper.cc",
     "clipboard/custom_data_helper.h",
     "clipboard/custom_data_helper_linux.cc",
     "clipboard/custom_data_helper_mac.mm",
     "clipboard/scoped_clipboard_writer.cc",
     "clipboard/scoped_clipboard_writer.h",
     "cocoa/animation_utils.h",
     "cocoa/appkit_utils.h",
     "cocoa/appkit_utils.mm",
     "cocoa/base_view.h",
@@ skipping 837 matching lines @@
     deps += [
       "//chromeos",
       "//ui/aura:test_support",
       "//ui/events:gesture_detection",
       "//ui/chromeos:ui_chromeos",
     ]
   }
 }
 }
 # TODO(GYP) Mac (ui_unittest_bundle) and Android (ui_unittests_apk).