Disable SDK constraint checking on bleeding edge.

utils/pub/sdk.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// Operations relative to the user's installed Dart SDK.
 library sdk;
 
 import 'dart:io';
 
 import 'package:pathos/path.dart' as path;
@@ skipping 19 matching lines @@
 
   var pubDir = path.dirname(new Options().script);
   dir = path.normalize(path.join(pubDir, "../../"));
   log.fine("Located SDK at $dir");
   return dir;
 }
 
 /// Gets the SDK's revision number formatted to be a semantic version.
 Version version = _getVersion();
 
+/// Is `true` if the current SDK is an unreleased bleeding edge version.
+bool get isBleedingEdge {
+  // The live build is locked to the magical old number "0.1.2+<stuff>".
+  return version.major == 0 && version.minor == 1 && version.patch == 2;
+}
+
 /// Determine the SDK's version number.
 Version _getVersion() {
   var revisionPath = path.join(rootDirectory, "version");
   var version = readTextFile(revisionPath).trim();
 
   // Given a version file like: 0.1.2.0_r17495
   // We create a semver like:   0.1.2+0.r17495
   var match = _versionPattern.firstMatch(version);
   if (match == null) {
     throw new FormatException("The Dart SDK's 'version' file was not in a "
         "format pub could recognize. Found: $version");
   }
 
   // Semantic versions cannot use "_".
   var build = match[4].replaceAll('_', '.');
 
   return new Version(
       int.parse(match[1]), int.parse(match[2]), int.parse(match[3]),
       build: build);
 }