Exclude "drt" from expected failures due to issue #23612.

Exclude "drt" from expected failures due to issue #23612.

On the "dartium-full" buildbots we use the "drt" runtime, which has
the same behavior as the "dartium" runtime.  So we need to exclude
this runtime for the same reason as we had to exclude "dartium" in
commit 046123935a10bb7b8bf85c69f3e8e6ca3a51b34e.

TBR=scheglov@google.com

Committed: https://github.com/dart-lang/sdk/commit/97ed10eba08e3578bb4365020606e392d44f5659

[Paul Berry, 2015-06-10 01:58:17]

Committed patchset #1 (id:1) manually as
97ed10eba08e3578bb4365020606e392d44f5659 (presubmit successful).

[scheglov, 2015-06-10 03:27:31]

lgtm