Revert "Revert "Disable the irregexp backend.""

This reverts commit http://code.google.com/p/dart/source/detail?r=42240
Reason for revert: failures and timeouts on Dartium bots.

TBR=fschneider@google.com
BUG=

Review URL: https://codereview.chromium.org//792853002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42246 260f80e4-7a28-3924-810f-c04153c831b5
dart2js: don't pass the supername to visitFields.

R=sigurdm@google.com

Review URL: https://codereview.chromium.org//761483002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42247 260f80e4-7a28-3924-810f-c04153c831b5
Test for FieldElement.isEnumConstant

R=brianwilkerson@google.com

Review URL: https://codereview.chromium.org//790083002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42248 260f80e4-7a28-3924-810f-c04153c831b5
New getter: FieldElement.isEnumConstant (Dart version of source)

R=brianwilkerson@google.com

Review URL: https://codereview.chromium.org//790103002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42249 260f80e4-7a28-3924-810f-c04153c831b5
Instrument communications

R=danrubel@google.com, lukechurch@google.com, scheglov@google.com

Review URL: https://codereview.chromium.org//790063002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42250 260f80e4-7a28-3924-810f-c04153c831b5
Add MacOS content_shell download to homebrew formula update app.

BUG=dartbug.com/21717
R=ricow@google.com

Review URL: https://codereview.chromium.org//788043004

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42251 260f80e4-7a28-3924-810f-c04153c831b5
Code clean-up

R=scheglov@google.com

Review URL: https://codereview.chromium.org//792053002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42252 260f80e4-7a28-3924-810f-c04153c831b5