Switch SignatureVerifier to taking an algorithm enum.

components/crx_file.gypi

 # 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': 'crx_file',
       'type': 'static_library',
       'dependencies': [
         '../base/base.gyp:base',
         '../crypto/crypto.gyp:crypto',
       ],
       'include_dirs': [
         '..',
       ],
       'sources': [
-        'crx_file/constants.h',
         'crx_file/crx_file.cc',
         'crx_file/crx_file.h',
         'crx_file/id_util.cc',
         'crx_file/id_util.h',
       ],
     },
   ],
 }