Move exception support to its own library

pkg/analyzer/lib/src/task/manager.dart

 // Copyright (c) 2015, 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 analyzer.src.task.manager;
 
 import 'dart:collection';
 
-import 'package:analyzer/src/generated/java_engine.dart';
+import 'package:analyzer/exception/exception.dart';
 import 'package:analyzer/task/model.dart';
 
 /**
  * An object that manages the information about the tasks that have been
  * defined.
  */
 class TaskManager {
   /**
    * A table mapping [ResultDescriptor]s to a list of [TaskDescriptor]s
    * for the tasks that can be used to compute the result.
@@ skipping 94 matching lines @@
       TaskSuitability suitability = descriptor.suitabilityFor(target);
       if (suitability == TaskSuitability.HIGHEST) {
         return descriptor;
       } else if (best == null && suitability == TaskSuitability.LOWEST) {
         best = descriptor;
       }
     }
     return best;
   }
 }