Make it possible to test command buffer decoder functions with extension flags

gpu/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.
 
 # GYP-to-GN project mappings:
 #
 #  gpu.gyp:command_buffer_client => //gpu/command_buffer/client
 #
 #  gpu.gyp:command_buffer_common => //gpu/command_buffer/common
 #
@@ skipping 160 matching lines @@
     "command_buffer/service/gles2_cmd_decoder_unittest_1_autogen.h",
     "command_buffer/service/gles2_cmd_decoder_unittest_2.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_2_autogen.h",
     "command_buffer/service/gles2_cmd_decoder_unittest_3.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_3_autogen.h",
     "command_buffer/service/gles2_cmd_decoder_unittest_async_pixel.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_base.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_base.h",
     "command_buffer/service/gles2_cmd_decoder_unittest_context_state.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_drawing.cc",
+    "command_buffer/service/gles2_cmd_decoder_unittest_extensions.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_framebuffers.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_programs.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_textures.cc",
     "command_buffer/service/gles2_cmd_decoder_unittest_attribs.cc",
     "command_buffer/service/gl_surface_mock.cc",
     "command_buffer/service/gl_surface_mock.h",
     "command_buffer/service/gpu_scheduler_unittest.cc",
     "command_buffer/service/gpu_service_test.cc",
     "command_buffer/service/gpu_service_test.h",
     "command_buffer/service/id_manager_unittest.cc",
@@ skipping 53 matching lines @@
   ]
 
   deps = [
     "//base",
     "//base/third_party/dynamic_annotations",
     "//testing/gmock",
     "//testing/gtest",
     "//third_party/angle:translator_static",
   ]
 }