Rename mash_shell to mash_session.

mash/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.
 
 import("//testing/test.gni")
 
 # Target that builders build.
 group("all") {
   testonly = true
 
   deps = [
     ":tests",
     "//components/leveldb",
     "//mash/example",
     "//mash/init",
     "//mash/login",
     "//mash/screenlock",
-    "//mash/shell",
+    "//mash/session",
     "//mash/task_viewer",
   ]
 }
 
 group("tests") {
   testonly = true
 
   deps = [
     ":mash_unittests",
     "//mash/wm:tests",
   ]
 }
 
 test("mash_unittests") {
   deps = [
     "//base",
     "//base/test:run_all_unittests",
     "//base/test:test_config",
     "//base/test:test_support",
     "//mash/wm:unittests",
     "//mojo/platform_handle:platform_handle_impl",
   ]
 }