Create a "PackageRef" class that defines a versionless package reference.

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

Index: sdk/lib/_internal/pub/test/version_solver_test.dart
diff --git a/sdk/lib/_internal/pub/test/version_solver_test.dart b/sdk/lib/_internal/pub/test/version_solver_test.dart
index 380803a0c29e14155526cf9bff84a280a3c69e90..6c2cb22784290651e90b911bf57aef1b9cb9575b 100644
--- a/sdk/lib/_internal/pub/test/version_solver_test.dart
+++ b/sdk/lib/_internal/pub/test/version_solver_test.dart
@@ -940,8 +940,8 @@ Package mockPackage(String description, String version,
   var sdkConstraint = null;
 
   // Build the pubspec dependencies.
-  var dependencies = <PackageRef>[];
-  var devDependencies = <PackageRef>[];
+  var dependencies = <PackageDep>[];
+  var devDependencies = <PackageDep>[];
 
   dependencyStrings.forEach((name, constraint) {
     parseSource(name, (isDev, name, source) {
@@ -953,12 +953,12 @@ Package mockPackage(String description, String version,
         return;
       }
 
-      var ref = new PackageRef(packageName, source, constraint, name);
+      var dep = new PackageDep(packageName, source, constraint, name);
 
       if (isDev) {
-        devDependencies.add(ref);
+        devDependencies.add(dep);
       } else {
-        dependencies.add(ref);
+        dependencies.add(dep);
       }
     });
   });