Initial support for build_runner build (#3)

Supports a subset of arguments to pass through to the build command.

webdev/bin/webdev.dart

@@ -0,0 +1,7 @@
+import 'dart:async';
+
+import 'package:webdev/webdev.dart';
+
+Future main(List<String> args) async {
+  await webdevCommandRunner().run(args);
+}

webdev/lib/src/command/build_command.dart

@@ -0,0 +1,38 @@
+import 'dart:async';
+import 'package:io/io.dart';
+
+import 'package:args/command_runner.dart';
+
+/// Command to execute pub run build_runner build.
+class BuildCommand extends Command {
+  @override
+  final name = 'build';
+
+  @override
+  final description = 'Run builders to build a package.';
+
+  BuildCommand() {
+    // TODO(nshahan) Expose more args passed to build_runner build.
+    // build_runner might expose args for use in wrapping scripts like this one.
+    argParser
+      ..addOption('output',
+          abbr: 'o', help: 'A directory to write the result of a build to.')
+      ..addFlag('verbose',
+          abbr: 'v',
+          defaultsTo: false,
+          negatable: false,
+          help: 'Enables verbose logging.');
+  }
+
+  @override
+  Future run() async {
+    final manager = new ProcessManager();
+    final executable = 'pub';
+    final arguments = ['run', 'build_runner', 'build', '--assume-tty'];
+    arguments.addAll(argResults.arguments);
+    var spawn = await manager.spawn(executable, arguments);
+
+    await spawn.exitCode;
+    await sharedStdIn.terminate();
+  }
+}

webdev/lib/src/webdev_command_runner.dart

@@ -0,0 +1,13 @@
+import 'package:args/command_runner.dart';
+
+import 'command/build_command.dart';
+
+/// All available top level commands.
+CommandRunner webdevCommandRunner() {
+  final commandRunner =
+      new CommandRunner('webdev', 'A tool to develop Dart web projects.');
+
+  commandRunner.addCommand(new BuildCommand());
+
+  return commandRunner;
+}

webdev/lib/webdev.dart

@@ -0,0 +1 @@
+export 'src/webdev_command_runner.dart';

webdev/pubspec.yaml

@@ -6,5 +6,9 @@ homepage: https://github.com/dart-lang/webdev
 environment:
   sdk: ">=2.0.0-dev <2.0.0"
 
+dependencies:
+  args: ^1.2.0
+  io: ^0.3.1
+
 dev_dependencies:
   test: "^0.12.0"