Add --checked flag to mojo_run that runs sky_viewer in checked mode

Also refactors the command line assembling to make a bit more sense.

Fixes #53

packages/flutter_tools/lib/src/run_mojo.dart

@@ -7,7 +7,6 @@ library sky_tools.run_mojo;
 import 'dart:async';
 import 'dart:io';
 
-import 'package:args/args.dart';
 import 'package:args/command_runner.dart';
 import 'package:logging/logging.dart';
 import 'package:path/path.dart' as path;
@@ -17,11 +16,14 @@ import 'process.dart';
 
 final Logger _logging = new Logger('sky_tools.run_mojo');
 
+enum _MojoConfig { Debug, Release }
+
 class RunMojoCommand extends Command {
   final name = 'run_mojo';
   final description = 'Run a Flutter app in mojo.';
   RunMojoCommand() {
     argParser.addFlag('android', negatable: false, help: 'Run on an Android device');
+    argParser.addFlag('checked', negatable: false, help: 'Run Flutter in checked mode');
     argParser.addFlag('mojo-debug', negatable: false, help: 'Use Debug build of mojo');
     argParser.addFlag('mojo-release', negatable: false, help: 'Use Release build of mojo (default)');
 
@@ -38,12 +40,12 @@ class RunMojoCommand extends Command {
     return file.absolute.path;
   }
 
-  Future<int> _runAndroid(ArgResults results, String appPath) async {
+  Future<int> _runAndroid(String mojoPath, _MojoConfig mojoConfig, String appPath, List<String> additionalArgs) async {
     String skyViewerUrl = ArtifactStore.googleStorageUrl('viewer', 'android-arm');
-    String command = await _makePathAbsolute(path.join(results['mojo-path'], 'mojo', 'devtools', 'common', 'mojo_run'));
+    String command = await _makePathAbsolute(path.join(mojoPath, 'mojo', 'devtools', 'common', 'mojo_run'));
     String appName = path.basename(appPath);
     String appDir = path.dirname(appPath);
-    String buildFlag = argResults['mojo-debug'] ? '--debug' : '--release';
+    String buildFlag = mojoConfig == _MojoConfig.Debug ? '--debug' : '--release';
     List<String> args = [
       '--android',
       buildFlag,
@@ -58,19 +60,19 @@ class RunMojoCommand extends Command {
         args.add('--verbose');
       }
     }
-    args.addAll(results.rest);
+    args.addAll(additionalArgs);
     return runCommandAndStreamOutput(command, args);
   }
 
-  Future<int> _runLinux(ArgResults results, String appPath) async {
+  Future<int> _runLinux(String mojoPath, _MojoConfig mojoConfig, String appPath, List<String> additionalArgs) async {
     String viewerPath = await _makePathAbsolute(await ArtifactStore.getPath(Artifact.SkyViewerMojo));
-    String mojoBuildType = argResults['mojo-debug'] ? 'Debug' : 'Release';
-    String mojoShellPath = await _makePathAbsolute(path.join(results['mojo-path'], 'out', mojoBuildType, 'mojo_shell'));
+    String mojoBuildType = mojoConfig == _MojoConfig.Debug ? 'Debug' : 'Release';
+    String mojoShellPath = await _makePathAbsolute(path.join(mojoPath, 'out', mojoBuildType, 'mojo_shell'));
     List<String> args = [
       'file://${appPath}',
       '--url-mappings=mojo:sky_viewer=file://${viewerPath}'
     ];
-    args.addAll(results.rest);
+    args.addAll(additionalArgs);
     return runCommandAndStreamOutput(mojoShellPath, args);
   }
 
@@ -84,11 +86,18 @@ class RunMojoCommand extends Command {
       _logging.severe('Cannot specify both --mojo-debug and --mojo-release');
       return 1;
     }
+    List<String> args = [];
+    if (argResults['checked']) {
+      args.add('--args-for=mojo:sky_viewer --enable-checked-mode');
+    }
+    String mojoPath = argResults['mojo-path'];
+    _MojoConfig mojoConfig = argResults['mojo-debug'] ? _MojoConfig.Debug : _MojoConfig.Release;
     String appPath = await _makePathAbsolute(argResults['app']);
+
     if (argResults['android']) {
-      return _runAndroid(argResults, appPath);
+      return _runAndroid(mojoPath, mojoConfig, appPath, args);
     } else {
-      return _runLinux(argResults, appPath);
+      return _runLinux(mojoPath, mojoConfig, appPath, args);
     }
   }
 }