Fix some GN component build issues.

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 18 matching lines @@
 #  command_buffer/command_buffer.gyp:gles2_utils =>
 #     //gpu/command_buffer/common
 #     (Merged in to here because the separate file exists in GYP only to break
 #     a .gyp file dependency cycle which GN doesn't have.)
 #
 # gpu/skia_bindings/skia_bindings.gyp:gpu_skia_bindings => //gpu/skia_bindings
 
 import("//testing/test.gni")
 import("//build/config/ui.gni")
 
+config("gpu_implementation") {
+  defines = [ "GPU_IMPLEMENTATION" ]
+}
+
 component("gpu") {
   public_deps = [
     "//gpu/command_buffer/client",
     "//gpu/command_buffer/client:gles2_cmd_helper_sources",
     "//gpu/command_buffer/common",
     "//gpu/command_buffer/service",
     "//gpu/config",
     "//gpu/ipc",
   ]
 }
 
 source_set("test_support") {
   testonly = true
   sources = [
     "command_buffer/client/gles2_interface_stub.cc",
     "command_buffer/client/gles2_interface_stub.h",
     "command_buffer/service/error_state_mock.cc",
     "command_buffer/service/gles2_cmd_decoder_mock.cc",
   ]
 
+  configs += [ ":gpu_implementation" ]
+
   public_deps = [
     ":gpu",
     "//gpu/command_buffer/client:gles2_interface",
   ]
   deps = [
     "//testing/gmock",
     "//testing/gtest",
     "//ui/gl:gl_unittest_utils",
   ]
 }
@@ skipping 231 matching lines @@
     libs = [ "GL" ]
 
     configs += [ "//build/config/linux:x11" ]
 
     deps = [
       "//base",
       "//ui/gl",
     ]
   }
 }