Disable chrome://downloads ui for Android.

chrome/chrome_browser.gypi

 # 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.
 
 {
   'targets': [
     {
       'target_name': 'browser',
       'type': 'static_library',
       'variables': { 'enable_wexit_time_destructors': 1, },
@@ skipping 4426 matching lines @@
             'browser/ui/window_sizer.h',
             'browser/ui/webui/ntp/ntp_resource_cache.cc',
           ],
           'sources/': [
             ['exclude', '^browser/importer/'],
             ['exclude', '^browser/printing/'],
             ['exclude', '^browser/themes/'],
             ['exclude', '^browser/ui/panels/'],
             ['exclude', '^browser/ui/tabs/'],
             ['exclude', '^browser/ui/toolbar/'],
+            ['exclude', '^browser/ui/webui/downloads_'],
             ['exclude', '^browser/ui/webui/options'],
             ['exclude', '^browser/ui/webui/options2'],
             ['exclude', '^browser/ui/webui/print_preview/'],
             ['exclude', '^browser/ui/webui/sync_promo'],
           ],
         }],
         ['OS=="mac"', {
           'sources!': [
             'browser/automation/automation_provider_list_generic.cc',
             'browser/bookmarks/bookmark_drop_info.cc',
@@ skipping 881 matching lines @@
          'variables': {
           'proto_in_dir': '../third_party/cros_system_api/dbus/',
           'proto_out_dir': 'chrome/browser/chromeos/dbus',
          },
          'includes': ['../build/protoc.gypi'],
         }],
       ],
     },
   ],
 }