Run dart2js tests unmodified in drt.

dart/lib/compiler/implementation/js_backend/emitter.dart

Index: dart/lib/compiler/implementation/js_backend/emitter.dart
diff --git a/dart/lib/compiler/implementation/js_backend/emitter.dart b/dart/lib/compiler/implementation/js_backend/emitter.dart
index 3c146c527d2313d654345332a7cf0577e2806f2a..4567d376996fd57482023081176fccba8761c6dd 100644
--- a/dart/lib/compiler/implementation/js_backend/emitter.dart
+++ b/dart/lib/compiler/implementation/js_backend/emitter.dart
@@ -332,6 +332,14 @@ function(prototype, staticName, fieldName, getterName, lazyValue) {
     buffer.add("$isolate = $finishIsolateConstructorName($isolate);\n");
   }
 
+  /**
+   * Generate stubs to handle invocation of methods with optional
+   * arguments.
+   *
+   * A method like [: foo([x]) :] may be invoked by the following
+   * calls: [: foo(), foo(1), foo(x: 1) :]. See the sources of this
+   * function for detailed examples.
+   */
   void addParameterStub(FunctionElement member,
                         Selector selector,
                         DefineMemberFunction defineInstanceMember) {
@@ -1226,20 +1234,37 @@ $mainEnsureGetter
       mainCall = '${namer.isolateAccess(main)}()';
     }
     buffer.add("""
+
+//
+// BEGIN invoke [main].
+//
 if (typeof document != 'undefined' && document.readyState != 'complete') {
   document.addEventListener('readystatechange', function () {
     if (document.readyState == 'complete') {
-      ${mainCall};
+      if (typeof dartMainRunner == 'function') {
+        dartMainRunner(function() { ${mainCall}; });
+      } else {
+        ${mainCall};
+      }
     }
   }, false);
 } else {
-  ${mainCall};
+  if (typeof dartMainRunner == 'function') {
+    dartMainRunner(function() { ${mainCall}; });
+  } else {
+    ${mainCall};
+  }
 }
+//
+// END invoke [main].
+//
+
 """);
   }
 
   String assembleProgram() {
     measure(() {
+      mainBuffer.add(HOOKS_API_USAGE);
       mainBuffer.add('function ${namer.ISOLATE}() {}\n');
       mainBuffer.add('init();\n\n');
       // Shorten the code by using "$$" as temporary.
@@ -1308,3 +1333,14 @@ if (typeof document != 'undefined' && document.readyState != 'complete') {
 }
 
 typedef void DefineMemberFunction(String invocationName, CodeBuffer definition);
+
+const String HOOKS_API_USAGE = """
+// Generated by dart2js, the Dart to JavaScript compiler.
+// The code supports the following hooks:
+// dartPrint(message)   - if this function is defined it is called
+//                        instead of the Dart [print] method.
+// dartMainRunner(main) - if this function is defined, the Dart [main]
+//                        method will not be invoked directly.
+//                        Instead, a closure that will invoke [main] is
+//                        passed to [dartMainRunner].
+""";