Made HashMap.update faster by reducing it to one lookup.
Made HashMap.update faster by reducing it to one lookup.

fixes https://github.com/dart-lang/sdk/issues/48866

Test=ci and golem

Change-Id: Ia56bd5b5de83dc8f7263eeda27e7abd3af42851e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/242120
Reviewed-by: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@google.com>
Commit-Queue: Siva Annamalai <2e618a8cbd7bb6b3d4409061ae407d692a098546@google.com>
Reviewed-by: Lasse Nielsen <80295e4ef244a07779f93eaa95d582bad8e316a5@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk