Add --hot-reload-rollback test mode

tools/testing/dart/test_suite.dart

Index: tools/testing/dart/test_suite.dart
diff --git a/tools/testing/dart/test_suite.dart b/tools/testing/dart/test_suite.dart
index 5dfbd393c5bae9e6787bacfbaef2ee0db30ea143..2c4b54102a06c1324a17eaef27b04e122e5a7a25 100644
--- a/tools/testing/dart/test_suite.dart
+++ b/tools/testing/dart/test_suite.dart
@@ -300,7 +300,7 @@ abstract class TestSuite {
       return;
     }
 
-    if (configuration['hot_reload']) {
+    if (configuration['hot_reload'] || configuration['hot_reload_rollback']) {
       // Handle reload special cases.
       if (expectations.contains(Expectation.COMPILETIME_ERROR)) {
         // Running a test that expects a compilation error with hot reloading
@@ -850,7 +850,8 @@ class StandardTestSuite extends TestSuite {
                             buildDir,
                             suiteDir,
                             createTestCase,
-                            configuration['hot_reload']));
+                            (configuration['hot_reload'] ||
+                             configuration['hot_reload_rollback'])));
     } else {
       createTestCase(filePath, filePath, optionsFromFile['hasCompileError'],
           optionsFromFile['hasRuntimeError'],