Add --hot-reload-test-mode flag to embedder and wire it up to test.py

tools/testing/dart/compiler_configuration.dart

Index: tools/testing/dart/compiler_configuration.dart
diff --git a/tools/testing/dart/compiler_configuration.dart b/tools/testing/dart/compiler_configuration.dart
index 4e129e81b6c085566c960dfcddb88d2d11a27bbd..76a0e5577764e0821831e205bfba20ff427f21b4 100644
--- a/tools/testing/dart/compiler_configuration.dart
+++ b/tools/testing/dart/compiler_configuration.dart
@@ -179,8 +179,9 @@ class NoneCompilerConfiguration extends CompilerConfiguration {
       args.add('--enable_type_checks');
     }
     if (hotReload) {
-      args.add('--identity-reload');
-      args.add('--reload-every=100000');
+      args.add('--hot-reload-test-mode');
+      // Remove the following once known bugs with background compilation
+      // and OSR are fixed.
       args.add('--no-background-compilation');
       args.add('--no-osr');
     }