Add unitAboutToCompile() into DartCompilerListener

compiler/javatests/com/google/dart/corelib/SharedTestCase.java

Index: compiler/javatests/com/google/dart/corelib/SharedTestCase.java
diff --git a/compiler/javatests/com/google/dart/corelib/SharedTestCase.java b/compiler/javatests/com/google/dart/corelib/SharedTestCase.java
index 9be4ecb9bf0ed75ea3cc3dedac277ef6abb569ad..81d745ae234a64a73e815a0badae3c8289fd3226 100644
--- a/compiler/javatests/com/google/dart/corelib/SharedTestCase.java
+++ b/compiler/javatests/com/google/dart/corelib/SharedTestCase.java
@@ -5,7 +5,6 @@
 package com.google.dart.corelib;
 
 import com.google.dart.compiler.CommandLineOptions.CompilerOptions;
-import com.google.dart.compiler.ast.DartUnit;
 import com.google.dart.compiler.CompilerConfiguration;
 import com.google.dart.compiler.DartArtifactProvider;
 import com.google.dart.compiler.DartCompilationError;
@@ -218,7 +217,7 @@ public abstract class SharedTestCase extends TestCase {
   }
 
   private DartCompilerListener getListener() {
-    DartCompilerListener listener = new DartCompilerListener() {
+    DartCompilerListener listener = new DartCompilerListener.Empty() {
       @Override
       public void onError(DartCompilationError event) {
         if (event.getErrorCode().getSubSystem() == SubSystem.STATIC_TYPE) {
@@ -240,10 +239,6 @@ public abstract class SharedTestCase extends TestCase {
           throw new AssertionError(event);
         }
       }
-
-      @Override
-      public void unitCompiled(DartUnit unit) {
-      }
     };
     return listener;
   }