Implement modular compilation

lib/src/codegen/html_codegen.dart

-// Copyright (c) 2015, 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.
-
-import 'package:html/dom.dart';
-import 'package:html/parser.dart' show parseFragment;
-import 'package:logging/logging.dart' show Logger;
-
-// TODO(jmesserly): the string interpolation in these could lead to injection
-// bugs. Not really a security issue since input is trusted, but the resulting
-// parse tree may not match expectations if interpolated strings contain quotes.
-
-/// A script tag that loads the .js code for a compiled library.
-Node libraryInclude(String jsUrl) =>
-    parseFragment('<script src="$jsUrl"></script>\n');
-
-/// A script tag that invokes the main function on the entry point library.
-Node invokeMain(String mainLibraryName) {
-  var code = mainLibraryName == null
-      ? 'console.error("dev_compiler error: main was not generated");'
-      // TODO(vsm): Can we simplify this?
-      // See: https://github.com/dart-lang/dev_compiler/issues/164
-      : "dart_library.start('$mainLibraryName');";
-  return parseFragment('<script>$code</script>\n');
-}
-
-final _log = new Logger('dev_compiler.src.codegen.html_codegen');