Use HTTP response headers for PNaCl caching instead of bitcode hash.

ppapi/native_client/src/trusted/plugin/plugin.gypi

 # Copyright (c) 2012 The Native Client 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.
     'common_sources': [
       'file_downloader.cc',
       'file_utils.cc',
       'json_manifest.cc',
       'local_temp_file.cc',
       'module_ppapi.cc',
+      'nacl_http_response_headers.cc',
       'nacl_subprocess.cc',
       'plugin.cc',
       'pnacl_coordinator.cc',
       'pnacl_options.cc',
       'pnacl_resources.cc',
       'pnacl_translate_thread.cc',
       'scriptable_plugin.cc',
       'sel_ldr_launcher_chrome.cc',
       'service_runtime.cc',
       'srpc_client.cc',
@@ skipping 81 matching lines @@
         'link_settings': {
           'libraries': [
             '-lgdi32.lib',
             '-luser32.lib',
           ],
         },
       }],
     ],
   },
 }