Ignore lockfile entries where the source is wrong.

utils/pub/version_solver.dart

Index: utils/pub/version_solver.dart
diff --git a/utils/pub/version_solver.dart b/utils/pub/version_solver.dart
index c00cda5f533ff5a1e3766a335eb47abb0c7cf588..3cb3230b9a9f5af3c33726d35a82a0e9385f00dd 100644
--- a/utils/pub/version_solver.dart
+++ b/utils/pub/version_solver.dart
@@ -183,7 +183,8 @@ class VersionSolver {
     for (var dependerName in dependency.dependers) {
       var depender = getDependency(dependerName);
       var locked = lockFile.packages[dependerName];
-      if (locked != null && depender.version == locked.version) {
+      if (locked != null && depender.version == locked.version &&
+          lockedPackage.source.name == dep.source.name) {
         enqueue(new UnlockPackage(depender));
         return true;
       }
@@ -360,7 +361,7 @@ abstract class ChangeConstraint implements WorkItem {
     // If the dependency is on a package in the lockfile, use the lockfile's
     // version for that package if it's valid given the other constraints.
     var lockedPackage = solver.lockFile.packages[name];
-    if (lockedPackage != null) {
+    if (lockedPackage != null && newDependency.source == lockedPackage.source) {
       var lockedVersion = lockedPackage.version;
       if (newConstraint.allows(lockedVersion)) {
         solver.enqueue(