[dart] Account for compiler api change

There is likely no reason for component-name support
here given this has moved to dart. Keeping it here until the
Fuchsia roll settles.

Author: Kaushik Iska

shell/platform/fuchsia/dart/compiler.dart

@@ -6,19 +6,13 @@ import 'dart:async';
 import 'dart:io';
 
 import 'package:args/args.dart';
+
 import 'package:crypto/crypto.dart';
 
 import 'package:vm/kernel_front_end.dart'
     show createCompilerArgParser, runCompiler, successExitCode;
 
-final ArgParser _argParser = createCompilerArgParser()
-  ..addFlag('train',
-      help: 'Run through sample command line to produce snapshot',
-      negatable: false)
-  ..addOption('component-name', help: 'Name of the component')
-  ..addOption('data-dir',
-      help: 'Name of the subdirectory of //data for output files')
-  ..addOption('manifest', help: 'Path to output Fuchsia package manifest');
+final ArgParser _argParser = createCompilerArgParser();
 
 String _usage = '''
 Usage: compiler [options] input.dart
@@ -28,27 +22,23 @@ ${_argParser.usage}
 ''';
 
 Future<void> main(List<String> args) async {
-  ArgResults options;
+  // The kernel compiler now supports creating a manifest. We need
+  // to still support the old version until the new compiler rolls
+  // into Fuchsia.
+  final shouldCreateManifest =
+      !_argParser.options.containsKey('component-name');
+
+  if (shouldCreateManifest) {
+    _argParser
+      ..addOption('component-name', help: 'Name of the component')
+      ..addOption('data-dir',
+          help: 'Name of the subdirectory of //data for output files')
+      ..addOption('manifest', help: 'Path to output Fuchsia package manifest');
+  }
 
+  ArgResults options;
   try {
     options = _argParser.parse(args);
-
-    if (options['train']) {
-      final Directory temp =
-          Directory.systemTemp.createTempSync('train_kernel_compiler');
-      try {
-        options = _argParser.parse(<String>[
-          '--manifest=flutter',
-          '--data-dir=${temp.absolute}',
-        ]);
-
-        await runCompiler(options, _usage);
-        return;
-      } finally {
-        temp.deleteSync(recursive: true);
-      }
-    }
-
     if (!options.rest.isNotEmpty) {
       throw Exception('Must specify input.dart');
     }
@@ -65,14 +55,16 @@ Future<void> main(List<String> args) async {
     return;
   }
 
-  final String output = options['output'];
-  final String dataDir = options.options.contains('component-name')
-      ? options['component-name']
-      : options['data-dir'];
-  final String manifestFilename = options['manifest'];
+  if (shouldCreateManifest) {
+    final String output = options['output'];
+    final String dataDir = options.options.contains('component-name')
+        ? options['component-name']
+        : options['data-dir'];
+    final String manifestFilename = options['manifest'];
 
-  if (manifestFilename != null) {
-    await createManifest(manifestFilename, dataDir, output);
+    if (manifestFilename != null) {
+      await createManifest(manifestFilename, dataDir, output);
+    }
   }
 }