Improve position information.

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

Index: pkg/front_end/lib/src/fasta/source/outline_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/source/outline_builder.dart b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
index 70598467aace9f575568ef08832229764b526ae9..bd2a56981c0921ad635d678c697f7522e315d2f2 100644
--- a/pkg/front_end/lib/src/fasta/source/outline_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
@@ -159,11 +159,11 @@ class OutlineBuilder extends UnhandledListener {
   @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);
   }
@@ -395,7 +395,8 @@ class OutlineBuilder extends UnhandledListener {
     debugEvent("MixinApplication");
     List<TypeBuilder> mixins = pop();
     TypeBuilder supertype = pop();
-    push(library.addMixinApplication(supertype, mixins, -1));
+    push(
+        library.addMixinApplication(supertype, mixins, withKeyword.charOffset));
   }
 
   @override