mus: Split the gpu client-lib into a separate component.

services/ui/public/cpp/gpu/BUILD.gn

+# Copyright 2016 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/ui.gni")
+
+source_set("gpu") {
+  sources = [
+    "gpu_service.h",
+  ]
+
+  deps = [
+    ":internal",
+    "//gpu/ipc/client",
+    "//services/ui/public/interfaces",
+  ]
+
+  allow_circular_includes_from = [ ":internal" ]
+}
+
+source_set("internal") {
+  visibility = [
+    ":gpu",
+    "//services/ui/demo:lib",
+  ]
+
+  sources = [
+    "gpu_service.cc",
+    "mojo_gpu_memory_buffer_manager.cc",
+    "mojo_gpu_memory_buffer_manager.h",
+  ]
+
+  deps = [
+    "//base",
+    "//gpu/command_buffer/client",
+    "//gpu/ipc/client",
+    "//mojo/public/cpp/system",
+    "//services/service_manager/public/cpp",
+    "//services/ui/common:mus_common",
+    "//services/ui/public/interfaces",
+  ]
+}