Use the VM to detect when a precompiled executable is out-of-date.

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

Index: sdk/lib/_internal/pub/test/test_pub.dart
diff --git a/sdk/lib/_internal/pub/test/test_pub.dart b/sdk/lib/_internal/pub/test/test_pub.dart
index d2e958939f6b8a00ae1c3de732b55814756a5a84..a5ffe843ef3d4d784b9bb5f31d273c8c62893da1 100644
--- a/sdk/lib/_internal/pub/test/test_pub.dart
+++ b/sdk/lib/_internal/pub/test/test_pub.dart
@@ -825,6 +825,10 @@ Map packageMap(String name, String version, [Map dependencies]) {
   return package;
 }
 
+/// Resolves [target] relative to the path to pub's `test/asset` directory.
+String testAssetPath(String target) =>
+    p.join(p.dirname(libraryPath('test_pub')), 'asset', target);
+
 /// Returns a Map in the format used by the pub.dartlang.org API to represent a
 /// package version.
 ///