Don't use ThreadSignalBlocker in mac eventhandler.

Turns out kevent can modify the current sigmask.

BUG=
R=ricow@google.com

Review URL: https://codereview.chromium.org//212193002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@34408 260f80e4-7a28-3924-810f-c04153c831b5
2 files changed