Fix tests to run in dart-lang/sdk.

lib/src/io.dart

Index: lib/src/io.dart
diff --git a/lib/src/io.dart b/lib/src/io.dart
index 45a26a11669bc644303ca70a8beae56bf35299e7..d24ede0203bd1b4c4aaebdd722e5bd904515ce3e 100644
--- a/lib/src/io.dart
+++ b/lib/src/io.dart
@@ -515,9 +515,19 @@ final _dartRepoRegExp = new RegExp(
 
 /// Whether pub is running from source in the Dart repo.
 ///
-/// This can happen when building Observatory, for example.
-final bool runningFromDartRepo =
-    Platform.script.path.contains(_dartRepoRegExp);
+/// This can happen when running tests against the repo, as well as when
+/// building Observatory.
+final bool runningFromDartRepo = (() {
+  if (runningAsTestRunner) {
+    // When running from the test runner, we can't find our location via
+    // Platform.script since the runner munges that. However, it guarantees that
+    // the working directory is <repo>/third_party/pkg/pub.
+    return path.current.contains(
+        new RegExp(r"[/\\]third_party[/\\]pkg[/\\]pub$"));
+  } else {
+    return Platform.script.path.contains(_dartRepoRegExp);
+  }
+})();
 
 /// Resolves [target] relative to the path to pub's `asset` directory.
 String assetPath(String target) => runningFromSdk
@@ -569,6 +579,12 @@ final String dartRepoRoot = (() {
     throw new StateError("Not running from source in the Dart repo.");
   }
 
+  if (runningAsTestRunner) {
+    // When running in test code started by the test runner, the working
+    // directory will always be <repo>/third_party/pkg/pub.
+    return path.dirname(path.dirname(path.dirname(path.current)));
+  }
+
   // Get the URL of the repo root in a way that works when either both running
   // as a test or as a pub executable.
   var url = Platform.script.replace(