Add debug names to scopes.

pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
index b46efb28d340fd8d7ffd9bc2c15e0a78e4d1ed10..926b2423fdcad194c3f69ac4053c3230c9224ebc 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
@@ -134,14 +134,14 @@ class KernelLibraryBuilder
     Map<String, MemberBuilder> constructors = declaration.constructors;
     Map<String, MemberBuilder> setters = declaration.setters;
 
-    Scope classScope = new Scope(
-        members, setters, scope.withTypeVariables(typeVariables),
+    Scope classScope = new Scope(members, setters,
+        scope.withTypeVariables(typeVariables), "class $className",
         isModifiable: false);
 
     // When looking up a constructor, we don't consider type variables or the
     // library scope.
-    Scope constructorScope =
-        new Scope(constructors, null, null, isModifiable: false);
+    Scope constructorScope = new Scope(constructors, null, null, "constructors",
+        isModifiable: false);
     ClassBuilder cls = new SourceClassBuilder(
         documentationComment,
         metadata,
@@ -254,8 +254,9 @@ class KernelLibraryBuilder
           interfaces,
           new Scope(<String, MemberBuilder>{}, <String, MemberBuilder>{},
               scope.withTypeVariables(typeVariables),
+              "mixin $name", isModifiable: false),
+          new Scope(constructors, null, null, "constructors",
               isModifiable: false),
-          new Scope(constructors, null, null, isModifiable: false),
           this,
           <ConstructorReferenceBuilder>[],
           charOffset,