mb_config: Add official_optimize for android_cronet_release_trybot_arm64

This config makes a difference for test suite to pass or not.
See crbug.com/1115229#c51. So add it the trybot config.

Bug: 1115229
Change-Id: Ib7c738608ebc2ff6e92d6287b38ea52354254fa5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2380103
Auto-Submit: Haiyang Pan <hypan@google.com>
Reviewed-by: Erik Staab <estaab@chromium.org>
Commit-Queue: Erik Staab <estaab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#802379}

tools/mb/mb_config.pyl

@@ -1188,7 +1188,8 @@
     ],
 
     'android_cronet_release_trybot_arm64': [
-      'android', 'cronet_android', 'release_trybot', 'arm64', 'strip_debug_info',
+      'android', 'cronet_android', 'official_optimize', 'release_trybot', 'arm64',
+      'strip_debug_info',
     ],
 
     'android_debug_bot': [