Adding //third_party/auto to WebRTC DEPS file.

Starting from https://chromium-review.googlesource.com/750645, 
Chromium started to depend on //third-party/auto in order to use
an errorprone plugin that disallows the usage of synchronized public
methods.

Bug: webrtc:8491
Change-Id: Ie9bb70520fc713dc294050c8a536ce5091b8339c
No-Try: True
Reviewed-on: https://webrtc-review.googlesource.com/20002
Reviewed-by: Edward Lemur <ehmaldonado@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20556}
diff --git a/DEPS b/DEPS
index 299d0ec..08c54cf 100644
--- a/DEPS
+++ b/DEPS
@@ -61,6 +61,10 @@
     'url': Var('chromium_git') + '/android_tools.git' + '@' + 'ca0bd083872ad925881736fe2bedc3ff855e08f5',
     'condition': 'checkout_android',
   },
+  'src/third_party/auto/src': {
+    'url': Var('chromium_git') + '/external/github.com/google/auto.git' + '@' + '71802f2ae74dae2744abd999f8434e13055c4ee3',
+    'condition': 'checkout_android',
+  },
   'src/third_party/boringssl/src':
     Var('boringssl_git') + '/boringssl.git' + '@' +  Var('boringssl_revision'),
   'src/third_party/catapult':