Disable SDK constraint checking on bleeding edge.

utils/pub/solver/backtracking_solver.dart

Index: utils/pub/solver/backtracking_solver.dart
diff --git a/utils/pub/solver/backtracking_solver.dart b/utils/pub/solver/backtracking_solver.dart
index 4e5baa07ed5a46835cd85bb659527e02c33d5b14..a5e3e3c5b4ea4a8df3dc16dc121b7e7146601af5 100644
--- a/utils/pub/solver/backtracking_solver.dart
+++ b/utils/pub/solver/backtracking_solver.dart
@@ -588,6 +588,12 @@ class Traverser {
 /// Ensures that if [pubspec] has an SDK constraint, then it is compatible
 /// with the current SDK. Throws a [SolverFailure] if not.
 void _validateSdkConstraint(Pubspec pubspec) {
+  // If the user is running a continouous build of the SDK, just disable SDK
+  // constraint checking entirely. The actual version number you get is
+  // impossibly old and not correct. We'll just assume users on continuous
+  // know what they're doing.
+  if (sdk.isBleedingEdge) return;
+
   if (pubspec.environment.sdkVersion.allows(sdk.version)) return;
 
   throw new CouldNotSolveException(