Convert unittest to use "package:" imports.

tools/testing/dart/browser_test.dart

Index: tools/testing/dart/browser_test.dart
diff --git a/tools/testing/dart/browser_test.dart b/tools/testing/dart/browser_test.dart
index 0694db3f68f07c4c5bbbe1bc3a4276df21a1d252..619b8c70fc5fbca4f9a8dad843d6b2e1c5695c1f 100644
--- a/tools/testing/dart/browser_test.dart
+++ b/tools/testing/dart/browser_test.dart
@@ -54,12 +54,19 @@ library libraryWrapper;
 part '$test';
 """;
 
-String dartTestWrapper(Path dartHome, Path library) =>
-"""
+String dartTestWrapper(Path dartHome, Path library) {
+  // Tests inside "pkg" import unittest using "package:". All others use a
+  // relative path. The imports need to agree, so use a matching form here.
+  var unitTest = dartHome.append("pkg/unittest/lib").toString();
+  if (library.relativeTo(dartHome).segments().contains("pkg")) {
+    unitTest = 'package:unittest';
+  }
+
+  return """
 library test;
 
-import '${dartHome.append('pkg/unittest/lib/unittest.dart')}' as unittest;
-import '${dartHome.append('pkg/unittest/lib/html_config.dart')}' as config;
+import '$unitTest/unittest.dart' as unittest;
+import '$unitTest/html_config.dart' as config;
 import '${library}' as Test;
 
 main() {
@@ -67,4 +74,4 @@ main() {
   unittest.group('', Test.main);
 }
 """;
-
+}