This reverts commit 038e981f89.
Reason for revert: Breaks some tests; visible changes to some web UIs.
Original change's description:
> Fix duration.toString() to conform the description
>
> Duration.toString() should return in a format of "HH:MM:SS.mmmmmm".
> But when `hours` is less than 10, toString() doesn't have the leading
> zero, which is "H:MM:SS.mmmmmm".
>
> The corresponding co19 issue: https://github.com/dart-lang/co19/issues/733
>
> Bug: https://github.com/dart-lang/sdk/issues/41737
> Change-Id: I2264171b2b37e89056695f7f821125a5f78d87fb
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/151163
> Commit-Queue: Zichang Guo <zichangguo@google.com>
> Reviewed-by: Lasse R.H. Nielsen <lrn@google.com>
TBR=lrn@google.com,zichangguo@google.com
# Not skipping CQ checks because original CL landed > 1 day ago.
Bug: https://github.com/dart-lang/sdk/issues/41737
Change-Id: I4d7ef5de9807e8e2b2a77c2171d1693b7527f671
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/151848
Reviewed-by: David Morgan <davidmorgan@google.com>
Commit-Queue: David Morgan <davidmorgan@google.com>
1d3fbbed7c