Convert some GN test support targets to static libs.

ui/message_center/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/features.gni")
 import("//build/config/ui.gni")
 import("//testing/test.gni")
 
 # TODO(msw|mukai|dewittj): Move ash-specific files: crbug.com/585175
 component("message_center") {
@@ skipping 148 matching lines @@
       sources += [
         "notification.cc",
         "notification.h",
         "notifier_settings.cc",
         "notifier_settings.h",
       ]
     }
   }
 }
 
-source_set("test_support") {
+static_library("test_support") {
   testonly = true
 
   if (enable_notifications && !is_android) {
     sources = [
       "fake_message_center.cc",
       "fake_message_center.h",
       "fake_message_center_tray_delegate.cc",
       "fake_message_center_tray_delegate.h",
       "fake_notifier_settings_provider.cc",
       "fake_notifier_settings_provider.h",
@@ skipping 68 matching lines @@
         # Compositor is needed by message_center_view_unittest.cc and for the
         # fonts used by bounded_label_unittest.cc.
         "//ui/compositor",
         "//ui/display",
         "//ui/views",
         "//ui/views:test_support",
       ]
     }
   }  # enable_notifications && !is_android
 }