Snapshot DDC trained on itself

pkg/dev_compiler/lib/src/compiler/command.dart

 // Copyright (c) 2016, 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.
 
 import 'dart:io';
 import 'package:analyzer/src/command_line/arguments.dart'
     show
         defineAnalysisArguments,
         filterUnknownArguments,
         ignoreUnrecognizedFlagsFlag;
@@ skipping 143 matching lines @@
     _usageException('Number of output files (${outPaths.length}) must match '
         'number of module formats (${moduleFormats.length}).');
   }
 
   // TODO(jmesserly): for now the first one is special. This will go away once
   // we've removed the "root" and "module name" variables.
   var firstOutPath = outPaths[0];
 
   var libraryRoot = argResults['library-root'] as String;
   if (libraryRoot != null) {
-    libraryRoot = path.absolute(libraryRoot);
+    libraryRoot = path.canonicalize(libraryRoot);
   } else {
     libraryRoot = Directory.current.path;
   }
   var moduleRoot = argResults['module-root'] as String;
   String modulePath;
   if (moduleRoot != null) {
-    moduleRoot = path.absolute(moduleRoot);
+    moduleRoot = path.canonicalize(moduleRoot);
     if (!path.isWithin(moduleRoot, firstOutPath)) {
       _usageException('Output file $firstOutPath must be within the module '
           'root directory $moduleRoot');
     }
     modulePath =
         path.withoutExtension(path.relative(firstOutPath, from: moduleRoot));
   } else {
     moduleRoot = path.dirname(firstOutPath);
     modulePath = path.basenameWithoutExtension(firstOutPath);
   }
@@ skipping 72 matching lines @@
 }
 
 void _usageException(String message) {
   throw new UsageException(message, _usageMessage);
 }
 
 /// Thrown when the input source code has errors.
 class CompileErrorException implements Exception {
   toString() => '\nPlease fix all errors before compiling (warnings are okay).';
 }