Add more components to the GN build.

components/sessions.gypi

 # Copyright (c) 2013 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': [
     {
+      # GN version: //components/sessions
       'target_name': 'sessions',
       'type': '<(component)',
       'dependencies': [
         '../base/base.gyp:base',
         '../content/content.gyp:content_browser',
         '../skia/skia.gyp:skia',
         '../third_party/protobuf/protobuf.gyp:protobuf_lite',
         '../url/url.gyp:url_lib',
       ],
       'include_dirs': [
         '..',
       ],
       'defines': [
         'SESSIONS_IMPLEMENTATION',
       ],
       'sources': [
+        # Note: sources list duplicated in GN build.
         'sessions/serialized_navigation_entry.cc',
         'sessions/serialized_navigation_entry.h',
       ],
       'conditions': [
         ['android_webview_build == 0', {
           'dependencies': [
              '../sync/sync.gyp:sync',
           ]
         }],
       ],
     },
     {
+      # GN version: //components/sessions:test_support
       'target_name': 'sessions_test_support',
       'type': 'static_library',
       'defines!': ['SESSIONS_IMPLEMENTATION'],
       'dependencies': [
         '../skia/skia.gyp:skia',
         '../testing/gtest.gyp:gtest',
       ],
       'include_dirs': [
         '..',
       ],
       'sources': [
+        # Note: sources list duplicated in GN build.
         'sessions/serialized_navigation_entry_test_helper.cc',
         'sessions/serialized_navigation_entry_test_helper.h',
       ],
       'conditions': [
         ['android_webview_build == 0', {
           'dependencies': [
              '../sync/sync.gyp:sync',
           ]
         }],
       ],
     },
   ],
 }