Move mojo\shell to services\shell

mojo/services/tracing/public/cpp/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.
 
 source_set("cpp") {
   sources = [
     "switches.cc",
     "switches.h",
     "trace_provider_impl.cc",
     "trace_provider_impl.h",
     "tracing_impl.cc",
     "tracing_impl.h",
   ]
 
   deps = [
     "//base",
     "//mojo/public/cpp/bindings",
     "//mojo/services/tracing/public/interfaces",
-    "//mojo/shell/public/cpp",
+    "//services/shell/public/cpp",
   ]
 }