Expect pub to live in pkg_tested in the SDK repo.

lib/src/io.dart

Index: lib/src/io.dart
diff --git a/lib/src/io.dart b/lib/src/io.dart
index 10a08b644c53865078c6323a6ce3f454c21bcc4e..92259fd5ae34c57933b145c9d785d1cb39332505 100644
--- a/lib/src/io.dart
+++ b/lib/src/io.dart
@@ -497,7 +497,7 @@ final bool runningFromSdk =
 ///
 /// This can happen when building Observatory, for example.
 final bool runningFromDartRepo =
-    Platform.script.path.endsWith('/third_party/pkg/pub/bin/pub.dart');
+    Platform.script.path.endsWith('/third_party/pkg_tested/pub/bin/pub.dart');
 
 /// Resolves [target] relative to the path to pub's `asset` directory.
 String assetPath(String target) => runningFromSdk
@@ -546,7 +546,7 @@ final String dartRepoRoot = (() {
     throw new StateError("Not running from source in the Dart repo.");
   }
 
-  // In the Dart repo, the script is in "third_party/pkg/pub/bin".
+  // In the Dart repo, the script is in "third_party/pkg_tested/pub/bin".
   return path.dirname(path.dirname(path.dirname(path.dirname(path.dirname(
       path.fromUri(Platform.script))))));
 })();