[infra] Add count of test result messages sent to Pub/Sub
[infra] Add count of test result messages sent to Pub/Sub

Cut message size in half, to help address timeouts when processing messages.

Bug: https://github.com/dart-lang/dart_ci/issues/46
Change-Id: I3eb7470c7ae31297ed7ecf4879206a5c26b48b22
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/126651
Reviewed-by: Alexander Thomas <29642742b6693024c89de8232f2e2542cf7eedf7@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk