Allow dart2dart to output one file per library.

sdk/lib/_internal/compiler/implementation/dart2js.dart

 // Copyright (c) 2013, 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.cmdline;
 
 import 'dart:async'
     show Future, EventSink;
 import 'dart:io'
     show exit, File, FileMode, Platform, RandomAccessFile, FileSystemException,
@@ skipping 137 matching lines @@
     } else {
       path = extractParameter(arguments.current);
     }
     explicitOut = true;
     out = currentDirectory.resolve(nativeToUriPath(path));
     sourceMapOut = Uri.parse('$out.map');
   }
 
   setOutputType(String argument) {
     optionsImplyCompilation.add(argument);
-    if (argument == '--output-type=dart') {
+    if (argument == '--output-type=dart' ||
+        argument == '--output-type=dart-multi') {
       outputLanguage = OUTPUT_LANGUAGE_DART;
       if (!explicitOut) {
         out = currentDirectory.resolve('out.dart');
         sourceMapOut = currentDirectory.resolve('out.dart.map');
       }
     }
     passThrough(argument);
   }
 
   String getDepsOutput(Map<String, SourceFile> sourceFiles) {
@@ skipping 103 matching lines @@
   List<String> arguments = <String>[];
   List<OptionHandler> handlers = <OptionHandler>[
     new OptionHandler('-[chvm?]+', handleShortOptions),
     new OptionHandler('--throw-on-error(?:=[0-9]+)?', handleThrowOnError),
     new OptionHandler('--suppress-warnings', (_) {
       diagnosticHandler.showWarnings = false;
       passThrough('--suppress-warnings');
     }),
     new OptionHandler('--suppress-hints',
                       (_) => diagnosticHandler.showHints = false),
-    new OptionHandler('--output-type=dart|--output-type=js', setOutputType),
+    new OptionHandler(
+        '--output-type=dart|--output-type=dart-multi|--output-type=js',
+        setOutputType),
     new OptionHandler('--verbose', setVerbose),
     new OptionHandler('--version', (_) => wantVersion = true),
     new OptionHandler('--library-root=.+', setLibraryRoot),
     new OptionHandler('--out=.+|-o.*', setOutput, multipleArguments: true),
     new OptionHandler('--allow-mock-compilation', passThrough),
     new OptionHandler('--minify|-m', implyCompilation),
     new OptionHandler('--force-strip=.*', setStrip),
     new OptionHandler('--disable-diagnostic-colors',
                       (_) => diagnosticHandler.enableColors = false),
     new OptionHandler('--enable-diagnostic-colors',
@@ skipping 431 matching lines @@
       } else {
         print(">>> TEST FAIL");
       }
       stderr.writeln(">>> EOF STDERR");
       runJob();
     });
   }
 
   runJob();
 }