Fix multitest display name bug in test scripts.

BUG=
R=ricow@google.com

Review URL: https://codereview.chromium.org//702873002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@41520 260f80e4-7a28-3924-810f-c04153c831b5

tools/testing/dart/test_suite.dart

@@ -837,7 +837,8 @@ class StandardTestSuite extends TestSuite {
 
   void enqueueTestCaseFromTestInformation(TestInformation info) {
     String testName = buildTestCaseDisplayName(suiteDir, info.originTestPath,
-        multitestName: info.multitestKey);
+        multitestName:
+          info.optionsFromFile['isMultitest'] ? info.multitestKey : "");
     Set<Expectation> expectations = testExpectations.expectations(testName);
     if (info is HtmlTestInformation) {
       if (TestUtils.isBrowserRuntime(configuration['runtime'])) {