Allow multiple base::MessagePumpForUI instances to be created simultanenously on Windows.

base/base.gypi

Index: base/base.gypi
diff --git a/base/base.gypi b/base/base.gypi
index c8022844144feceb8816d93f0bea8579964347c9..5629dc49390bec4239f6da15757b06318d46d29a 100644
--- a/base/base.gypi
+++ b/base/base.gypi
@@ -539,8 +539,8 @@
           'nix/mime_util_xdg.h',
           'nix/xdg_util.cc',
           'nix/xdg_util.h',
-          'win/enum_variant.h',
           'win/enum_variant.cc',
+          'win/enum_variant.h',
           'win/event_trace_consumer.h',
           'win/event_trace_controller.cc',
           'win/event_trace_controller.h',
@@ -550,8 +550,10 @@
           'win/i18n.h',
           'win/iat_patch_function.cc',
           'win/iat_patch_function.h',
-          'win/iunknown_impl.h',
           'win/iunknown_impl.cc',
+          'win/iunknown_impl.h',
+          'win/message_window.cc',
+          'win/message_window.h',
           'win/metro.cc',
           'win/metro.h',
           'win/object_watcher.cc',
@@ -584,10 +586,10 @@
           'win/startup_information.h',
           'win/text_services_message_filter.cc',
           'win/text_services_message_filter.h',
-          'win/windows_version.cc',
-          'win/windows_version.h',
           'win/win_util.cc',
           'win/win_util.h',
+          'win/windows_version.cc',
+          'win/windows_version.h',
           'win/wrapped_window_proc.cc',
           'win/wrapped_window_proc.h',
         ],