Per discussion, implement the Omaha Client Update Protocol (CUP) in src/crypto.

google_apis/google_apis.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 1,  # Use higher warning level.
   },
   'includes': [
     '../build/win_precompile.gypi',
@@ skipping 30 matching lines @@
             'GOOGLE_CLIENT_ID_REMOTING="<(google_default_client_id)"',
           ]
         }],
         ['google_default_client_secret!=""', {
           'defines': [
             'GOOGLE_CLIENT_SECRET_MAIN="<(google_default_client_secret)"',
             'GOOGLE_CLIENT_SECRET_CLOUD_PRINT="<(google_default_client_secret)"',
             'GOOGLE_CLIENT_SECRET_REMOTING="<(google_default_client_secret)"',
           ]
         }],
+        [ 'OS == "android"', {
+            'dependencies': [
+              '../third_party/openssl/openssl.gyp:openssl',
+            ],
+            'sources/': [
+              ['exclude', 'cup/client_update_protocol_nss\.cc$'],
+            ],
+        }],
+        [ 'use_openssl==1', {
+            'sources!': [
+              'cup/client_update_protocol_nss.cc',
+            ],
+          }, {
+            'sources!': [
+              'cup/client_update_protocol_openssl.cc',
+            ],
+        },],
       ],
       'sources': [
+        'cup/client_update_protocol.cc',
+        'cup/client_update_protocol.h',
+        'cup/client_update_protocol_nss.cc',
+        'cup/client_update_protocol_openssl.cc',
         'gaia/gaia_auth_consumer.cc',
         'gaia/gaia_auth_consumer.h',
         'gaia/gaia_auth_fetcher.cc',
         'gaia/gaia_auth_fetcher.h',
         'gaia/gaia_auth_util.cc',
         'gaia/gaia_auth_util.h',
         'gaia/gaia_authenticator.cc',
         'gaia/gaia_authenticator.h',
         'gaia/gaia_constants.cc',
         'gaia/gaia_constants.h',
@@ skipping 15 matching lines @@
         'gaia/oauth2_mint_token_flow.cc',
         'gaia/oauth2_mint_token_flow.h',
         'google_api_keys.cc',
         'google_api_keys.h',
       ],
       # TODO(jschuh): crbug.com/167187 fix size_t to int truncations.
       'msvs_disabled_warnings': [4267, ],
     },
   ],
 }