Fix #269 - detect correctly generated files that are indirectly under the out

lib/component_build.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.
 
 /**
  * Common logic to make it easy to create a `build.dart` for your project.
  *
  * The `build.dart` script is invoked automatically by the Editor whenever a
  * file in the project changes. It must be placed in the root of a project
  * (where pubspec.yaml lives) and should be named exactly 'build.dart'.
@@ skipping 54 matching lines @@
       }
     }
   }
 }
 
 String _outDir(String file) =>
   new Path(file).directoryPath.append('out').toString();
 
 bool _isGeneratedFile(String filePath, List<Directory> outputDirs) {
   var path = new Path.fromNative(filePath);
+  var dirPrefix = path.directoryPath.toString();
   for (var dir in outputDirs) {
-    if (path.directoryPath.toString() == dir.path) return true;
+    if (dirPrefix.startsWith(dir.path)) return true;
   }
   return path.filename.startsWith('_');
 }
 
 bool _isInputFile(String path, List<Directory> outputDirs) {
   return (path.endsWith(".dart") || path.endsWith(".html"))
       && !_isGeneratedFile(path, outputDirs);
 }
 
 /** Delete all generated files. */
@@ skipping 25 matching lines @@
     ..addFlag("machine", negatable: false,
         help: "produce warnings in a machine parseable format")
     ..addFlag("help", negatable: false, help: "displays this help and exit");
   var args = parser.parse(arguments);
   if (args["help"]) {
     print(parser.getUsage());
     exit(0);
   }
   return args;
 }