Convert some GN test support targets to static libs.

ppapi/proxy/BUILD.gn

 # Copyright 2015 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/nacl/config.gni")
 
 config("proxy_implementation") {
   defines = [ "PPAPI_PROXY_IMPLEMENTATION" ]
 }
 
@@ skipping 340 matching lines @@
     "//gpu/ipc/common:command_buffer_traits",
     "//ipc",
     "//ppapi/c",
     "//ppapi/shared_impl",
   ]
   if (!is_nacl) {
     deps += [ "//skia" ]
   }
 }
 
-source_set("test_support") {
+static_library("test_support") {
   testonly = true
 
   sources = [
     "ppapi_proxy_test.cc",
     "ppapi_proxy_test.h",
     "resource_message_test_sink.cc",
     "resource_message_test_sink.h",
   ]
 
   public_deps = [
     ":proxy",
   ]
   deps = [
     "//base/test:test_support",
     "//ipc",
     "//ipc:test_support",
     "//ppapi/proxy",
     "//ppapi/shared_impl",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }