Fix trim methods returning a new string (instead of the argument) when
there's nothing to trim.
A second bug fixed in NEL handling in `trim`: the last line should be
`result.substring(...)` instead of `this.substring(...)`. The bug wasn't
caught by any of the tests: NEL needs to be handled specially on the
browser, but mixing NEL with other whitespace wasn't tested in the
existing tests `string_trim_test` and `string_trimlr_test`, so a new
test file added with this case.
Change-Id: Ibf84e185de1b26c9811e3ea58c2ad3f223da8515
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/363081
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Ömer Ağacan <omersa@google.com>
Reviewed-by: Lasse Nielsen <lrn@google.com>
