Add the 'docRange' property and use it to compute documentation comment.

pkg/analyzer/lib/src/generated/engine.dart

 // Copyright (c) 2014, 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 engine;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:math' as math;
 
@@ skipping 1623 matching lines @@
 
   @override
   String computeDocumentationComment(Element element) {
     if (element == null) {
       return null;
     }
     Source source = element.source;
     if (source == null) {
       return null;
     }
-    CompilationUnit unit = parseCompilationUnit(source);
-    if (unit == null) {
+    SourceRange docRange = element.docRange;
+    if (docRange == null) {
       return null;
     }
-    NodeLocator locator = new NodeLocator(element.nameOffset);
-    AstNode nameNode = locator.searchWithin(unit);
-    while (nameNode != null) {
-      if (nameNode is AnnotatedNode) {
-        Comment comment = nameNode.documentationComment;
-        if (comment == null) {
-          return null;
-        }
-        StringBuffer buffer = new StringBuffer();
-        List<Token> tokens = comment.tokens;
-        for (int i = 0; i < tokens.length; i++) {
-          if (i > 0) {
-            buffer.write("\n");
-          }
-          buffer.write(tokens[i].lexeme);
-        }
-        return buffer.toString();
-      }
-      nameNode = nameNode.parent;
-    }
-    return null;
+    String code = getContents(source).data;
+    String comment = code.substring(docRange.offset, docRange.end);
+    return comment.replaceAll('\r\n', '\n');
   }
 
   @override
   List<AnalysisError> computeErrors(Source source) {
     bool enableHints = _options.hint;
     bool enableLints = _options.lint;
 
     SourceEntry sourceEntry = _getReadableSourceEntry(source);
     if (sourceEntry is DartEntry) {
       List<AnalysisError> errors = new List<AnalysisError>();
@@ skipping 10391 matching lines @@
     PendingFuture pendingFuture =
         new PendingFuture<T>(_context, source, computeValue);
     if (!pendingFuture.evaluate(sourceEntry)) {
       _context._pendingFutureSources
           .putIfAbsent(source, () => <PendingFuture>[])
           .add(pendingFuture);
     }
     return pendingFuture.future;
   }
 }