Vendor python-rsa into build.

DEPS

 deps = {
   'build/scripts/gsd_generate_index':
     'https://chromium.googlesource.com/chromium/tools/gsd_generate_index.git',
   'build/scripts/private/data/reliability':
     'https://chromium.googlesource.com/chromium/src/chrome/test/data/reliability.git',
   'build/scripts/tools/deps2git':
     'https://chromium.googlesource.com/chromium/tools/deps2git.git',
   'build/third_party/gsutil':
     'https://chromium.googlesource.com/external/gsutil/src.git'
     '@5cba434b828da428a906c8197a23c9ae120d2636',
   'build/third_party/gsutil/boto':
     'https://chromium.googlesource.com/external/boto.git'
     '@98fc59a5896f4ea990a4d527548204fed8f06c64',
   'build/third_party/infra_libs':
     'https://chromium.googlesource.com/infra/infra/packages/infra_libs.git'
     '@a13e6745a4edd01fee683e4157ea0195872e64eb',
   'build/third_party/lighttpd':
     'https://chromium.googlesource.com/chromium/deps/lighttpd.git'
     '@9dfa55d15937a688a92cbf2b7a8621b0927d06eb',
   'build/third_party/pyasn1':
     'https://chromium.googlesource.com/external/github.com/etingof/pyasn1.git'
-    '@709cf013df8585956dda1a4fa2611bf10b91902b',
+    '@4181b2379eeae3d6fd9f4f76d0e6ae3789ed56e7',
   'build/third_party/pyasn1-modules':
     'https://chromium.googlesource.com/external/github.com/etingof/pyasn1-modules.git'
-    '@ea54a2e498277b85e3ee5f7a1bb0aeab7d1d013b',
+    '@956fee4f8e5fd3b1c500360dc4aa12dc5a766cb2',
+  'build/third_party/python-rsa':
+    'https://chromium.googlesource.com/external/github.com/sybrenstuvel/python-rsa.git'
+    '@version-3.1.4',
   'depot_tools':
     'https://chromium.googlesource.com/chromium/tools/depot_tools.git',
 }
 
 deps_os = {
   'unix': {
     'build/third_party/xvfb':
       'https://chromium.googlesource.com/chromium/tools/third_party/xvfb.git',
   },
 }
 
 hooks = [
   {
     "pattern": ".",
     "action": [
       "python", "-u", "build/scripts/common/remove_orphaned_pycs.py",
     ],
   },
   {
     "name": "cros_chromite",
     "pattern": r".*/cros_chromite_pins\.json",
     "action": [
       "python", "build/scripts/tools/runit.py", "python",
       "build/scripts/common/cros_chromite.py", "-v",
     ],
   },
 ]