Throw an error early when dump info is used with the startup emitter.

pkg/compiler/lib/src/compiler.dart

 // Copyright (c) 2012, 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.
 
 library dart2js.compiler_base;
 
 import 'dart:async' show EventSink, Future;
 
 import '../compiler_new.dart' as api;
 import 'cache_strategy.dart' show CacheStrategy;
@@ skipping 316 matching lines @@
           useNewSourceInfo: options.useNewSourceInfo);
       backend = jsBackend;
     } else {
       backend = new dart_backend.DartBackend(this, options.strips,
           multiFile: options.dart2dartMultiFile);
       if (options.dumpInfo) {
         throw new ArgumentError('--dump-info is not supported for dart2dart.');
       }
     }
 
+    if (options.dumpInfo && options.useStartupEmitter) {
+      throw new ArgumentError(
+          '--dump-info is not supported with the fast startup emitter');

[Harry Terkelsen, 2016/04/07 17:39:00]

I considered instead of crashing, just giving a warning and disabling dump-info
in this case, but I saw above that the compiler will crash if --dump-info is
enabled with dart2dart.

I'm open to either approach, let me know what you think

[Siggi Cherem (dart-lang), 2016/04/07 18:24:36]

fine with either too. This is probably easier to notice, so let's keep it.

+    }
+
     tasks = [
       dietParser = new DietParserTask(this, parsing.parserOptions),
       scanner = createScannerTask(),
       serialization = new SerializationTask(this),
       libraryLoader = new LibraryLoaderTask(
           this,
           new _ResolvedUriTranslator(this),
           new _ScriptLoader(this),
           new _ElementScanner(scanner),
           this.serialization,
@@ skipping 1721 matching lines @@
   _ElementScanner(this.scanner);
   void scanLibrary(LibraryElement library) => scanner.scanLibrary(library);
   void scanUnit(CompilationUnitElement unit) => scanner.scan(unit);
 }
 
 class _EmptyEnvironment implements Environment {
   const _EmptyEnvironment();
 
   String valueOf(String key) => null;
 }