mojo: first take on removing mojo_main_{chromium,standalone}.

mojo/public/cpp/application/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.
 
 source_set("base") {
   sources = [
     "application_impl.h",
     "connect.h",
     "lib/application_impl.cc",
     "lib/service_connector.cc",
     "lib/service_connector.h",
     "lib/application_connection.cc",
     "lib/application_delegate.cc",
     "lib/service_registry.cc",
     "lib/service_registry.h",
   ]
 
   deps = [
     "//mojo/public/cpp/bindings",
     "//mojo/public/interfaces/application",
   ]
 }
 
 source_set("chromium") {
   sources = [
-    "lib/application_impl_chromium.cc"
+    "lib/application_runner_chromium.cc"
   ]
 
   deps = [ ":base" ]
 }
 
 source_set("standalone") {
   sources = [
-    "lib/application_impl_standalone.cc"
+    "lib/application_runner.cc"
   ]
 
-  deps = [ ":base" ]
+  deps = [ 
+    ":base",
+    "//mojo/public/cpp/environment:standalone",
+  ]
 }
-
-source_set("main_chromium") {
-  sources = [
-    "lib/mojo_main_chromium.cc"
-  ]
-
-  deps = [ ":chromium" ]
-}
-
-source_set("main_standalone") {
-  sources = [
-    "lib/mojo_main_standalone.cc"
-  ]
-
-  deps = [ ":standalone" ]
-}