Improve position information.

pkg/front_end/lib/src/fasta/source/outline_builder.dart

 // Copyright (c) 2016, 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 fasta.outline_builder;
 
 import 'package:kernel/ast.dart' show ProcedureKind;
 
 import '../fasta_codes.dart' show FastaMessage, codeExpectedBlockToSkip;
 
@@ skipping 141 matching lines @@
   @override
   void handleRecoverExpression(Token token) {
     debugEvent("RecoverExpression");
     push(NullValue.Expression);
     push(token.charOffset);
   }
 
   @override
   void endPart(Token partKeyword, Token semicolon) {
     debugEvent("Part");
-    popCharOffset();
+    int charOffset = popCharOffset();
     String uri = pop();
     List<MetadataBuilder> metadata = pop();
     if (uri != null) {
-      library.addPart(metadata, uri);
+      library.addPart(metadata, uri, charOffset);
     }
     checkEmpty(partKeyword.charOffset);
   }
 
   @override
   void handleOperatorName(Token operatorKeyword, Token token) {
     debugEvent("OperatorName");
     push(operatorFromString(token.stringValue));
     push(token.charOffset);
   }
@@ skipping 211 matching lines @@
         nativeMethodName,
         isTopLevel: false);
     nativeMethodName = null;
   }
 
   @override
   void endMixinApplication(Token withKeyword) {
     debugEvent("MixinApplication");
     List<TypeBuilder> mixins = pop();
     TypeBuilder supertype = pop();
-    push(library.addMixinApplication(supertype, mixins, -1));
+    push(
+        library.addMixinApplication(supertype, mixins, withKeyword.charOffset));
   }
 
   @override
   void beginNamedMixinApplication(Token begin, Token name) {
     library.beginNestedDeclaration(name.lexeme, hasMembers: false);
   }
 
   @override
   void endNamedMixinApplication(Token beginToken, Token classKeyword,
       Token equals, Token implementsKeyword, Token endToken) {
@@ skipping 388 matching lines @@
   Link<Token> handleMemberName(Link<Token> identifiers) {
     if (!enableNative || identifiers.isEmpty) return identifiers;
     return removeNativeClause(identifiers);
   }
 
   @override
   void debugEvent(String name) {
     // printEvent(name);
   }
 }