Introduce getPrefixEndToken to avoid too big context in messages.

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;
 
@@ skipping 1841 matching lines @@
             return validateToken(from, to);
           }
         }
         return true;
       }, message: "Invalid current element: $currentElement [$begin,$end]."));
     }
     return new SourceSpan.fromTokens(uri, begin, end);
   }
 
   SourceSpan spanFromNode(Node node) {
-    return spanFromTokens(node.getBeginToken(), node.getEndToken());
+    return spanFromTokens(node.getBeginToken(), node.getPrefixEndToken());
   }
 
   SourceSpan spanFromElement(Element element) {
     if (element != null && element.sourcePosition != null) {
       return element.sourcePosition;
     }
     while (element != null && element.isSynthesized) {
       element = element.enclosingElement;
     }
     if (element != null &&
@@ skipping 317 matching lines @@
     if (_otherDependencies == null) {
       _otherDependencies = new Setlet<Element>();
     }
     _otherDependencies.add(element.implementation);
   }
 
   Iterable<Element> get otherDependencies {
     return _otherDependencies != null ? _otherDependencies : const <Element>[];
   }
 }