Add unitAboutToCompile() into DartCompilerListener

compiler/javatests/com/google/dart/compiler/type/TypeTestCase.java

Index: compiler/javatests/com/google/dart/compiler/type/TypeTestCase.java
diff --git a/compiler/javatests/com/google/dart/compiler/type/TypeTestCase.java b/compiler/javatests/com/google/dart/compiler/type/TypeTestCase.java
index c2af9ec776053445c35754896085db4cd4b0aae4..4e514964abb31d304536e40539ec4950fb8306d1 100644
--- a/compiler/javatests/com/google/dart/compiler/type/TypeTestCase.java
+++ b/compiler/javatests/com/google/dart/compiler/type/TypeTestCase.java
@@ -16,7 +16,6 @@ import com.google.dart.compiler.ast.DartMethodDefinition;
 import com.google.dart.compiler.ast.DartParameter;
 import com.google.dart.compiler.ast.DartStatement;
 import com.google.dart.compiler.ast.DartTypeNode;
-import com.google.dart.compiler.ast.DartUnit;
 import com.google.dart.compiler.ast.Modifiers;
 import com.google.dart.compiler.resolver.ClassElement;
 import com.google.dart.compiler.resolver.Elements;
@@ -163,15 +162,11 @@ abstract class TypeTestCase extends TestCase {
     checkNotSubtype(s, t);
   }
 
-  final DartCompilerListener listener = new DartCompilerListener() {
+  final DartCompilerListener listener = new DartCompilerListener.Empty() {
     @Override
     public void onError(DartCompilationError event) {
       throw new AssertionError(event);
     }
-
-    @Override
-    public void unitCompiled(DartUnit unit) {
-    }
   };
 
   final TestCompilerContext context = new TestCompilerContext() {