Issue 5157. Introduce TypeQuality. Try to find member in subclasses.

compiler/java/com/google/dart/compiler/type/InterfaceType.java

Index: compiler/java/com/google/dart/compiler/type/InterfaceType.java
diff --git a/compiler/java/com/google/dart/compiler/type/InterfaceType.java b/compiler/java/com/google/dart/compiler/type/InterfaceType.java
index aaf43ca3f781b37c80ca5b64e5b668bb73c79145..7a746c13108b56197fdeda4890e1e9b4b27ad244 100644
--- a/compiler/java/com/google/dart/compiler/type/InterfaceType.java
+++ b/compiler/java/com/google/dart/compiler/type/InterfaceType.java
@@ -32,6 +32,10 @@ public interface InterfaceType extends Type {
   InterfaceType asRawType();
 
   Member lookupMember(String name);
+  
+  void registerSubClass(ClassElement subClass);
+  void unregisterSubClass(ClassElement subClass);
+  Member lookupSubTypeMember(String name);
 
   interface Member {
     InterfaceType getHolder();