Allow OSExchangeData::Provider to be overridden at run time.

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 143 matching lines @@
     "dragdrop/drag_drop_types_win.cc",
     "dragdrop/drag_source_win.cc",
     "dragdrop/drag_source_win.h",
     "dragdrop/drag_utils_win.cc",
     "dragdrop/drop_target_event.cc",
     "dragdrop/drop_target_event.h",
     "dragdrop/drop_target_win.cc",
     "dragdrop/drop_target_win.h",
     "dragdrop/os_exchange_data.cc",
     "dragdrop/os_exchange_data.h",
+    "dragdrop/os_exchange_data_provider_builder_mac.h",
+    "dragdrop/os_exchange_data_provider_builder_mac.mm",
+    "dragdrop/os_exchange_data_provider_factory.cc",
+    "dragdrop/os_exchange_data_provider_factory.h",
     "dragdrop/os_exchange_data_provider_mac.h",
     "dragdrop/os_exchange_data_provider_mac.mm",
     "dragdrop/os_exchange_data_provider_win.cc",
     "dragdrop/os_exchange_data_provider_win.h",
     "hit_test.h",
     "l10n/formatter.cc",
     "l10n/formatter.h",
     "l10n/l10n_font_util.cc",
     "l10n/l10n_font_util.h",
     "l10n/l10n_util.cc",
@@ skipping 375 matching lines @@
     ]
   }
 
   if (!toolkit_views && !use_aura) {
     sources -= [
       "dragdrop/drag_drop_types.h",
       "dragdrop/drop_target_event.cc",
       "dragdrop/drop_target_event.h",
       "dragdrop/os_exchange_data.cc",
       "dragdrop/os_exchange_data.h",
+      "dragdrop/os_exchange_data_provider_factory.cc",
+      "dragdrop/os_exchange_data_provider_factory.h",
       "nine_image_painter_factory.cc",
       "nine_image_painter_factory.h",
     ]
   }
 
   if (is_android) {
     deps += [
       ":ui_base_jni_headers",
       "//ui/android:ui_java",
     ]
@@ skipping 380 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"
   }
 }