Add tool for viewing source maps.

tools/dart2js/sourceMapViewer/bin/source_map_viewer.dart

+// Copyright (c) 2014, 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 'dart:io';

[Johnni Winther, 2014/05/14 12:00:38]

Add blank line before import. Maybe add library tag.

[zarah, 2014/05/14 20:51:03]

Done.

+import 'package:http_server/http_server.dart' as http_server;
+import 'package:route/server.dart';
+import 'package:path/path.dart';
+import 'package:http_server/http_server.dart';
+
+/*
+ * This program serves a visualization of a JavaScript source map file generated
+ * by dart2js or pub.
+ *
+ * Usage: dart source_map_viewer.dart <path to map file>.
+ *
+ * The default system browser is started and pointed to the viewer if
+ * available.
+ */
+
+Directory rootDir = null;
+String sourceMapFile;
+
+void main(List<String> args) {
+  if (args.length != 1) {
+    print('One argument expected; the source map file.');
+    return;
+  }
+
+  File mapFile = new File(args[0]);
+  if (!mapFile.existsSync()) {
+    print('Map file not found at ${args[0]}');
+    return;

[ricow1, 2014/05/14 12:28:08]

I would set the exitCode to non zero here - it is good style to give non zero
exit code in case of failure (same above)

[zarah, 2014/05/14 20:51:03]

Done.

+  }
+
+  sourceMapFile = basename(mapFile.path);
+  rootDir = mapFile.parent;
+  startServer(rootDir);
+}
+
+// Sends the content of the file requested in the path parameter.
+void handleFile(HttpRequest request) {
+  String path = request.uri.queryParameters["path"];
+  if (path == null) {
+    request.response.close();
+    return;
+  }
+
+  path = rootDir.path + '/' + path;
+  new File(Uri.parse(path).toFilePath()).openRead()
+    .pipe(request.response).catchError((e) {
+    print("Error: $e");

[ricow1, 2014/05/14 12:28:08]

I would indent this 2 

[zarah, 2014/05/14 20:51:03]

Done.

+    request.response.close();
+  });
+}
+
+// Sends back the name of the source map file.
+void handleSourceMapFile(HttpRequest request) {
+  request.response.write(sourceMapFile);
+  request.response.close();
+}
+
+// Starts an HttpServer rooted in [dir] with two special routes, /file and /map.
+//
+// /file takes a parameter [path] and serves the content of the specified file
+//  in path relative to [dir]
+//
+// /map serves the name of the map file such that its content can be requested
+// with a /file request as above.
+void startServer(Directory dir) {
+  rootDir = dir;
+  int port = 9223;

[ricow1, 2014/05/14 12:28:08]

I would use an ephemeral port here, you can easily pass that to the startBrowser
call below 

[zarah, 2014/05/14 20:51:03]

Done.

+  HttpServer.bind(InternetAddress.LOOPBACK_IP_V4, port).then((server) {
+    print("Source mapping server is running on "
+           "'http://${server.address.address}:$port/'");
+    Router router = new Router(server)
+                ..serve('/file').listen(handleFile)
+                ..serve('/map').listen(handleSourceMapFile);
+
+    // Set up default handler. This will serve files from our 'build'
+    // directory. Disable jail root, as packages are local symlinks.
+    VirtualDirectory virDir = new http_server.VirtualDirectory(dir.path)
+      ..jailRoot = false
+      ..allowDirectoryListing = true;
+
+    virDir.directoryHandler = (dir, request) {
+      // Redirect directory requests to index.html files.
+      Uri indexUri = new Uri.file(dir.path).resolve('display.html');
+      virDir.serveFile(new File(indexUri.toFilePath()), request);
+    };
+
+    // Add an error page handler.
+    virDir.errorPageHandler = (HttpRequest request) {
+      print("Resource not found: ${request.uri.path}");
+      request.response.statusCode = HttpStatus.NOT_FOUND;
+      request.response.close();
+    };
+
+    // Serve everything not routed elsewhere through the virtual directory.
+    virDir.serve(router.defaultStream);
+
+    // Start the system' default browser
+    startBrowser('http://${server.address.address}:$port/');
+  });
+}
+
+startBrowser(String url) {
+  String command;
+  if (Platform.isWindows) {
+    command = 'start';

[Johnni Winther, 2014/05/14 12:00:38]

Change 'start' to 'cmd.exe /C start'.

[zarah, 2014/05/14 20:51:03]

Done.

+  } else if (Platform.isMacOS) {
+    command = 'open';
+  } else {
+    command = '/usr/bin/google-chrome';

[ricow1, 2014/05/14 12:28:08]

that is not really the default browser, you could try doing xdg-open and then
fall back to using chrome if it does not work

[zarah, 2014/05/14 20:51:03]

Done.

+  }
+
+  print('Starting browser: ${command} ${url}');
+  Process.run(command, ['$url']);

[ricow1, 2014/05/14 12:28:08]

You may want to get the output and print an error message if we could not launch
it

[zarah, 2014/05/14 20:51:03]

Done.

+}