Migrate GpuProcess to use MojoChild/ShellConnection for the Shell handshake

content/public/app/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.
 
 # App different than the regular content subcomponents (see comments in
 # //content/BUILD.gn) because it has to support the browser/child process split
 # (the "both" target include both browser and child process files and is used
 # for testing).
 #
 # In non-component mode, browser, child, and both all follow the same structure:
@@ skipping 143 matching lines @@
     "//media/mojo/services:media_manifest",
     "//services/user:manifest",
   ]
 }
 
 mojo_application_manifest("renderer_manifest") {
   type = "exe"
   application_name = "content_renderer"
   source = "mojo/content_renderer_manifest.json"
 }
+
+mojo_application_manifest("gpu_manifest") {
+  type = "exe"
+  application_name = "content_gpu"
+  source = "mojo/content_gpu_manifest.json"
+}