Use mnc-dr-arc-m55 branch for Android on R55

BUG=chromium:653935
TEST=None

Change-Id: Ia9ecbb95b169f0bfc20257821ed53b01d12f0b23
Reviewed-on: https://chromium-review.googlesource.com/399898
Reviewed-by: Bernie Thompson <bhthompson@chromium.org>
Commit-Queue: Bernie Thompson <bhthompson@chromium.org>
Tested-by: Bernie Thompson <bhthompson@chromium.org>
diff --git a/cbuildbot/constants.py b/cbuildbot/constants.py
index e994459..5a4ffb0 100644
--- a/cbuildbot/constants.py
+++ b/cbuildbot/constants.py
@@ -292,7 +292,7 @@
 INTERNAL_GERRIT_URL = 'https://%s' % INTERNAL_GERRIT_HOST
 
 ANDROID_BUCKET_URL = 'gs://android-build-chromeos/builds'
-ANDROID_BUILD_BRANCH = 'git_mnc-dr-arc-dev'
+ANDROID_BUILD_BRANCH = 'git_mnc-dr-arc-m55'
 ANDROID_BUILD_TARGETS = {
     # TODO(b/29509721): Workaround to roll adb with system image. We want to
     # get rid of this.