Fix SDK constraints in lockfiles.

lib/src/solver/version_solver.dart

Index: lib/src/solver/version_solver.dart
diff --git a/lib/src/solver/version_solver.dart b/lib/src/solver/version_solver.dart
index 55ecc3c5c25aa6a368236360c028d21a09949984..fba24418d2b27a7f6bc232f765b810d2890c6c7c 100644
--- a/lib/src/solver/version_solver.dart
+++ b/lib/src/solver/version_solver.dart
@@ -76,8 +76,12 @@ class SolveResult {
   /// The [LockFile] representing the packages selected by this version
   /// resolution.
   LockFile get lockFile {
-    var sdkConstraint = new VersionConstraint.intersection(
-        pubspecs.values.map((pubspec) => pubspec.environment.sdkVersion));
+    // Don't factor in overridden dependencies' SDK constraints, because we'll
+    // accept those packages even if their constraints don't match.
+    var sdkConstraint = new VersionConstraint.intersection(pubspecs.values
+        .where((pubspec) =>
+            !_root.dependencyOverrides.any((dep) => dep.name == pubspec.name))
+        .map((pubspec) => pubspec.environment.sdkVersion));
     return new LockFile(packages, _sources, sdkConstraint: sdkConstraint);
   }