Teach i18nTemplate.process() to handle <link rel=import> and <template>

ui/webui/resources/js/compiled_resources.gyp

 # 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.
 {
   'targets': [
     {
       'target_name': 'assert',
       'includes': ['../../../../third_party/closure_compiler/compile_js.gypi'],
     },
     {
@@ skipping 28 matching lines @@
       'includes': ['../../../../third_party/closure_compiler/compile_js.gypi'],
     },
     {
       'target_name': 'parse_html_subset',
       'includes': ['../../../../third_party/closure_compiler/compile_js.gypi'],
     },
     {
       'target_name': 'i18n_template_no_process',
       'variables': {
         'depends': ['compiled_resources.gyp:load_time_data'],
+        'externs': ['../../../../third_party/closure_compiler/externs/pending_compiler_externs.js'],
       },
       'includes': ['../../../../third_party/closure_compiler/compile_js.gypi'],
     },
     {
       'target_name': 'i18n_template',
       'variables': {
         'depends': ['compiled_resources.gyp:load_time_data'],
+        'externs': ['../../../../third_party/closure_compiler/externs/pending_compiler_externs.js'],
       },
       'includes': ['../../../../third_party/closure_compiler/compile_js.gypi'],
     },
   ],
 }