Add LanguageModel, a keyed service that collects language info from CLD.

components/translate/content/browser/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.
 
 import("//build/config/features.gni")
 
 static_library("browser") {
   sources = [
     "content_translate_driver.cc",
     "content_translate_driver.h",
+    "language_model_observer.cc",
+    "language_model_observer.h",
   ]
 
   public_deps = [
     "//base",
     "//components/translate/content/common",
     "//components/translate/core/browser",
     "//components/translate/core/common",
   ]
   deps = [
     "//content/public/browser",
     "//content/public/common",
     "//net",
   ]
 }