Disable SDK constraint checking on bleeding edge.

utils/pub/sdk.dart

Index: utils/pub/sdk.dart
diff --git a/utils/pub/sdk.dart b/utils/pub/sdk.dart
index 3222c9e9f8eeed863b7b69d2844e78ac60ace547..b9b50ecca2c7a1c2867fa340f81e734701292897 100644
--- a/utils/pub/sdk.dart
+++ b/utils/pub/sdk.dart
@@ -37,6 +37,12 @@ String get rootDirectory {
 /// 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");