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

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

Index: compiler/java/com/google/dart/compiler/type/InterfaceTypeUnion.java
diff --git a/compiler/java/com/google/dart/compiler/type/InterfaceTypeUnion.java b/compiler/java/com/google/dart/compiler/type/InterfaceTypeUnion.java
index 4fcf9a24a5390088c11bf7c51b970cdc2b3d9ac3..c3eca3b606ca9b66909949ff3670f4ad4321ae7a 100644
--- a/compiler/java/com/google/dart/compiler/type/InterfaceTypeUnion.java
+++ b/compiler/java/com/google/dart/compiler/type/InterfaceTypeUnion.java
@@ -51,8 +51,8 @@ class InterfaceTypeUnion implements InterfaceType {
   }
 
   @Override
-  public boolean isInferred() {
-    return false;
+  public TypeQuality getQuality() {
+    return TypeQuality.EXACT;
   }
 
   @Override
@@ -95,4 +95,17 @@ class InterfaceTypeUnion implements InterfaceType {
     }
     return null;
   }
+  
+  @Override
+  public void registerSubClass(ClassElement subClass) {
+  }
+  
+  @Override
+  public void unregisterSubClass(ClassElement subClass) {
+  }
+  
+  @Override
+  public Member lookupSubTypeMember(String name) {
+    return null;
+  }
 }