Rewrite pub's version solver.

sdk/lib/_internal/pub/test/implicit_barback_dependency_test.dart

Index: sdk/lib/_internal/pub/test/implicit_barback_dependency_test.dart
diff --git a/sdk/lib/_internal/pub/test/implicit_barback_dependency_test.dart b/sdk/lib/_internal/pub/test/implicit_barback_dependency_test.dart
index 9b7877478b3456bb65c5eab24d0e24bd287ef24b..0d16e51cd8c3ee09f179c89c5d87755409d793f8 100644
--- a/sdk/lib/_internal/pub/test/implicit_barback_dependency_test.dart
+++ b/sdk/lib/_internal/pub/test/implicit_barback_dependency_test.dart
@@ -135,8 +135,8 @@ main() {
     d.appDir({"barback": "any"}).create();
 
     pubGet(error: """
-Package barback 0.12.0 does not match >=$current <$max derived from:
-- myapp 0.0.0 depends on version any
+Package barback has no versions that match >=$current <$max derived from:
+- myapp depends on version any
 - pub itself depends on version >=$current <$max""");
   });
 
@@ -153,7 +153,7 @@ Package barback 0.12.0 does not match >=$current <$max derived from:
 
     pubGet(error: """
 Incompatible version constraints on barback:
-- myapp 0.0.0 depends on version $previous
+- myapp depends on version $previous
 - pub itself depends on version >=$current <$max""");
   });
 }