Restored the MirrorsUsed which was removed in CL 1933283002.

Restored the MirrorsUsed which was removed in CL 1933283002.

The `git cl land` on https://codereview.chromium.org/1915123008 seemed
to give rise to many timeout failures in the dart2js-jsshell columns of
the build bot; that CL was then reverted. However, it turns out to be
the removal of `@MirrorsUsed(metaTargets: 'ReflectiveTest')` in
https://codereview.chromium.org/1933283002 that causes the timeouts
(e.g., it changes an 11sec test run into a 64s test run, which violates
the timeout constraint of 60s on the bot).

BUG=

Committed: https://github.com/dart-lang/sdk/commit/21a1345fa8df19676b69e9d6fc4978d0c1a5ffc5

[eernst, 2016-05-02 08:42:29]

eernst@google.com changed reviewers:
+ scheglov@google.com

[eernst, 2016-05-02 08:42:29]

TBR:

Restores the `MirrorsUsed` which was removed in CL 1933283002, because that
caused many tests in dart2js-jsshell to fail. (I noticed this because CL
1915123008 was blamed).

[eernst, 2016-05-02 08:42:54]

Description was changed from

==========
Restored the MirrorsUsed which was removed in CL 1933283002.

The `git cl land` on https://codereview.chromium.org/1915123008 seemed
to give rise to many timeout failures in the dart2js-jsshell columns of
the build bot; that CL was then reverted. However, it turns out to be
the removal of `@MirrorsUsed(metaTargets: 'ReflectiveTest')` in
https://codereview.chromium.org/1933283002 that causes the timeouts
(e.g., it changes an 11sec test run into a 64s test run, which violates
the timeout constraint of 60s on the bot).

BUG=
==========

to

==========
Restored the MirrorsUsed which was removed in CL 1933283002.

The `git cl land` on https://codereview.chromium.org/1915123008 seemed
to give rise to many timeout failures in the dart2js-jsshell columns of
the build bot; that CL was then reverted. However, it turns out to be
the removal of `@MirrorsUsed(metaTargets: 'ReflectiveTest')` in
https://codereview.chromium.org/1933283002 that causes the timeouts
(e.g., it changes an 11sec test run into a 64s test run, which violates
the timeout constraint of 60s on the bot).

BUG=

Committed:
https://github.com/dart-lang/sdk/commit/21a1345fa8df19676b69e9d6fc4978d0c1a5ffc5
==========

[eernst, 2016-05-02 08:42:55]

Committed patchset #1 (id:1) manually as
21a1345fa8df19676b69e9d6fc4978d0c1a5ffc5 (presubmit successful).

[scheglov, 2016-05-02 13:51:51]

lgtm