Update incremental load example so you can point to different sdk

pkg/front_end/example/incremental_reload/run.dart

Index: pkg/front_end/example/incremental_reload/run.dart
diff --git a/pkg/front_end/example/incremental_reload/run.dart b/pkg/front_end/example/incremental_reload/run.dart
index 7fadbc7fb4a7012ef1eb9dabe5747a16345bcd3e..5a7f4da6bf76d5ccd84dea559faec50c7c860234 100644
--- a/pkg/front_end/example/incremental_reload/run.dart
+++ b/pkg/front_end/example/incremental_reload/run.dart
@@ -46,21 +46,41 @@ import 'dart:io';
 import 'dart:async';
 import 'dart:convert' show ASCII;
 
+import 'package:args/args.dart';
+
 import '../../tool/vm/reload.dart';
 
 import 'compiler_with_invalidation.dart';
 
+ArgParser argParser = new ArgParser(allowTrailingOptions: false)
+  ..addOption('sdk-root', help: 'Path to sdk for compilation')
+  ..addOption('input', help: 'Input dart file')

[Siggi Cherem (dart-lang), 2017/08/15 00:37:14]

minor suggestion: let's remove this option and use `options.rest` below to get
the input

[aam, 2017/08/15 03:59:49]

Done.

+  ..addOption('output', help: 'Output dill file', defaultsTo: 'out.dill');

[Siggi Cherem (dart-lang), 2017/08/15 00:37:15]

minor suggestion: let's add `abbr: "o"`

[aam, 2017/08/15 03:59:49]

Done.

+
+String usage = '''
+Usage: dart [options]
+
+Runs console-driven incremental compiler.
+
+Options:
+${argParser.usage}
+''';
+
 RemoteVm remoteVm = new RemoteVm();
 AnsiTerminal terminal = new AnsiTerminal();
 
 main(List<String> args) async {
-  if (args.length <= 1) {
-    print('usage: dart incremental_compile.dart input.dart out.dill');
+  ArgResults options = argParser.parse(args);
+  if (options['input'] == null) {
+    print('Need input file');
+    print(usage);
     exit(1);
   }
 
-  var compiler = await createIncrementalCompiler(args[0]);
-  var outputUri = Uri.base.resolve(args[1]);
+  var compiler = await createIncrementalCompiler(options['input'],
+      argSdkRoot:
+          options['sdk-root'] != null ? Uri.parse(options['sdk-root']) : null);
+  var outputUri = Uri.base.resolve(options['output']);
 
   showHeader();
   listenOnKeyPress(compiler, outputUri)
@@ -76,7 +96,7 @@ Future listenOnKeyPress(IncrementalCompiler compiler, Uri outputUri) {
     try {
       CompilationResult compilationResult;
       ReloadResult reloadResult;
-      switch (char) {
+      switch (char.trim()) {
         case 'r':
           compilationResult = await rebuild(compiler, outputUri);
           if (!compilationResult.errorSeen &&