Ensure locations are always provided, but don't store them yet.

pkg/front_end/lib/src/fasta/source/source_class_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.source_class_builder;
 
 import 'package:kernel/ast.dart' show
     Class,
     Constructor,
     Supertype,
+    TreeNode,
     setParents;
 
 import '../errors.dart' show
     internalError,
     inputError;
 
 import '../kernel/kernel_builder.dart' show
     Builder,
     ConstructorReferenceBuilder,
     KernelClassBuilder,
     KernelFieldBuilder,
     KernelFunctionBuilder,
     KernelLibraryBuilder,
     KernelProcedureBuilder,
     KernelTypeBuilder,
     KernelTypeVariableBuilder,
     LibraryBuilder,
     MemberBuilder,
     MetadataBuilder,
     ProcedureBuilder,
     TypeVariableBuilder;
 
 import '../dill/dill_member_builder.dart' show
     DillMemberBuilder;
 
+import '../util/relativize.dart' show
+    relativizeUri;
+
+Class initializeClass(Class cls, String name, LibraryBuilder parent,
+    int charOffset) {
+  cls ??= new Class(name: name);
+  cls.fileUri ??= relativizeUri(parent.fileUri);
+  if (cls.fileOffset != TreeNode.noOffset) {
+    cls.fileOffset = charOffset;
+  }
+  return cls;
+}
+
 class SourceClassBuilder extends KernelClassBuilder {
   final Class cls;
 
   final Map<String, Builder> constructors = <String, Builder>{};
 
   final Map<String, Builder> membersInScope;
 
   final List<ConstructorReferenceBuilder> constructorReferences;
 
   SourceClassBuilder(List<MetadataBuilder> metadata, int modifiers,
       String name, List<TypeVariableBuilder> typeVariables,
       KernelTypeBuilder supertype, List<KernelTypeBuilder>interfaces,
       Map<String, Builder> members, List<KernelTypeBuilder> types,
-      LibraryBuilder parent, this.constructorReferences, [Class cls])
-      : cls = cls ?? new Class(name: name),
+      LibraryBuilder parent, this.constructorReferences, int charOffset,
+      [Class cls])
+      : cls = initializeClass(cls, name, parent, charOffset),
         membersInScope = computeMembersInScope(members, name),
         super(metadata, modifiers, name, typeVariables, supertype, interfaces,
-            members, types, parent);
+            members, types, parent, charOffset);
 
   int resolveTypes(LibraryBuilder library) {
     int count = 0;
     if (typeVariables != null) {
       for (KernelTypeVariableBuilder t in typeVariables) {
         cls.typeParameters.add(t.parameter);
       }
       setParents(cls.typeParameters, cls);
       count += cls.typeParameters.length;
     }
@@ skipping 94 matching lines @@
       if (isConstructorName(builder.name, className)) return;
     }
     if (name.indexOf(".") != -1) {
       inputError(null, null, "Only constructors and factories can have names "
           "containing a period ('.'): $name");
     }
     membersInScope[name] = builder;
   });
   return membersInScope;
 }