Run dart2js tests unmodified in browser.

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

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
 class ClosureInvocationElement extends FunctionElement {
   ClosureInvocationElement(SourceString name,
@@ skipping 314 matching lines @@
     String name = finishIsolateConstructorName;
     String value = finishIsolateConstructorFunction;
     buffer.add("$name = $value;\n");
   }
 
   void emitFinishIsolateConstructorInvocation(CodeBuffer buffer) {
     String isolate = namer.ISOLATE;
     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) {
     FunctionSignature parameters = member.computeSignature(compiler);
     int positionalArgumentCount = selector.positionalArgumentCount;
     if (positionalArgumentCount == parameters.parameterCount) {
       assert(selector.namedArgumentCount == 0);
       return;
     }
     ConstantHandler handler = compiler.constantHandler;
@@ skipping 874 matching lines @@
     Element main = compiler.mainApp.find(Compiler.MAIN);
     String mainCall = null;
     if (compiler.isolateLibrary != null) {
       Element isolateMain =
         compiler.isolateLibrary.find(Compiler.START_ROOT_ISOLATE);
       mainCall = buildIsolateSetup(buffer, main, isolateMain);
     } else {
       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 "$$" as temporary.
       classesCollector = @"$$";
       mainBuffer.add('var $classesCollector = {};\n');
       // Shorten the code by using [namer.CURRENT_ISOLATE] as temporary.
       isolateProperties = namer.CURRENT_ISOLATE;
       mainBuffer.add('var $isolateProperties = $isolatePropertiesName;\n');
       emitClasses(mainBuffer);
       mainBuffer.add(boundClosureBuffer);
@@ skipping 48 matching lines @@
   }
 
   String buildSourceMap(CodeBuffer buffer, SourceFile compiledFile) {
     SourceMapBuilder sourceMapBuilder = new SourceMapBuilder();
     buffer.forEachSourceLocation(sourceMapBuilder.addMapping);
     return sourceMapBuilder.build(compiledFile);
   }
 }
 
 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].
+""";