Read overlay content when computing completions (issue 27887)

pkg/analysis_server/lib/src/services/completion/dart/uri_contributor.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 services.completion.contributor.dart.importuri;
 
 import 'dart:async';
 import 'dart:core';
 
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
@@ skipping 48 matching lines @@
       int end = uri.end;
       if (offset > start) {
         if (offset < end) {
           // Quoted non-empty string
           visitSimpleStringLiteral(uri);
         } else if (offset == end) {
           if (end == start + 1) {
             // Quoted empty string
             visitSimpleStringLiteral(uri);
           } else {
-            String data = request.source.contents.data;
+            String data = request.sourceContents;
             if (end == data.length) {
               String ch = data[end - 1];
               if (ch != '"' && ch != "'") {
                 // Insertion point at end of file
                 // and missing closing quote on non-empty string
                 visitSimpleStringLiteral(uri);
               }
             }
           }
         }
       } else if (offset == start && offset == end) {
-        String data = request.source.contents.data;
+        String data = request.sourceContents;
         if (end == data.length) {
           String ch = data[end - 1];
           if (ch == '"' || ch == "'") {
             // Insertion point at end of file
             // and missing closing quote on empty string
             visitSimpleStringLiteral(uri);
           }
         }
       }
     }
@@ skipping 122 matching lines @@
   }
 
   String _extractPartialUri(SimpleStringLiteral node) {
     if (request.offset < node.contentsOffset) {
       return null;
     }
     return node.literal.lexeme.substring(
         node.contentsOffset - node.offset, request.offset - node.offset);
   }
 }