Very simple version of Isolates.

runtime/bin/main.cc

Index: runtime/bin/main.cc
diff --git a/runtime/bin/main.cc b/runtime/bin/main.cc
index 5e475390a4f13be0a411f8a975dd853aef2a8872..b6e8ee9ef049bddb900a00b4559c829e0b5de546 100644
--- a/runtime/bin/main.cc
+++ b/runtime/bin/main.cc
@@ -881,16 +881,32 @@ int main(int argc, char** argv) {
       }
     } else {
       // Lookup and invoke the top level main function.
-      Dart_Handle main_args[1];
+      // The top-level function may accept up to two arguments:
+      //   main(List<String> args, var message).
+      // However most commonly it either accepts one (the args list) or
+      // none.
+      // If the message is optional, main(args, [message]), it is invoked with
+      // one argument only.
+      Dart_Handle main_args[2];
       main_args[0] = CreateRuntimeOptions(&dart_options);
+      main_args[1] = Dart_Null();
+      // First try with 1 argument.
       result = Dart_Invoke(library, DartUtils::NewString("main"), 1, main_args);
       // TODO(iposva): Return a special error type for mismatched argument
       // counts from Dart_Invoke to avoid the string comparison.
       const char* expected_error = "Dart_Invoke: wrong argument count for "
-          "function 'main': 1 passed, 0 expected.";
+          "function 'main': ";
+      intptr_t length = strlen(expected_error);
       if (Dart_IsError(result) &&
-          strcmp(expected_error, Dart_GetError(result)) == 0) {
-        result = Dart_Invoke(library, DartUtils::NewString("main"), 0, NULL);
+          strncmp(expected_error, Dart_GetError(result), length) == 0) {
+        // Try with two arguments.
+        result =
+            Dart_Invoke(library, DartUtils::NewString("main"), 2, main_args);
+        if (Dart_IsError(result) &&
+            strncmp(expected_error, Dart_GetError(result), length) == 0) {
+          // Finally try with 0 arguments.
+          result = Dart_Invoke(library, DartUtils::NewString("main"), 0, NULL);
+        }
       }
       if (Dart_IsError(result)) {
         return DartErrorExit(result);