Revert of Implement ui::ClipboardMus.

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/buildflag_header.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 import("//ui/base/ui_features.gni")
@@ skipping 56 matching lines @@
     "clipboard/clipboard_android.h",
     "clipboard/clipboard_mac.h",
     "clipboard/clipboard_mac.mm",
     "clipboard/clipboard_types.h",
     "clipboard/clipboard_util_mac.h",
     "clipboard/clipboard_util_mac.mm",
     "clipboard/clipboard_util_win.cc",
     "clipboard/clipboard_util_win.h",
     "clipboard/clipboard_win.cc",
     "clipboard/clipboard_win.h",
+    "clipboard/custom_data_helper_linux.cc",
     "clipboard/custom_data_helper_mac.mm",
     "cocoa/animation_utils.h",
     "cocoa/appkit_utils.h",
     "cocoa/appkit_utils.mm",
     "cocoa/base_view.h",
     "cocoa/base_view.mm",
     "cocoa/cocoa_base_utils.h",
     "cocoa/cocoa_base_utils.mm",
     "cocoa/command_dispatcher.h",
     "cocoa/command_dispatcher.mm",
@@ skipping 858 matching lines @@
 if (is_mac) {
   mac_framework_bundle("ui_unittests_framework") {
     testonly = true
     deps = [
       "//ui/resources:ui_test_pak_bundle_data",
     ]
     info_plist = "test/framework-Info.plist"
     output_name = "ui_unittests Framework"
   }
 }