Add unitAboutToCompile() into DartCompilerListener

editor/tools/plugins/com.google.dart.tools.core_test/src/com/google/dart/tools/core/internal/compiler/TestCompilerListener.java

Index: editor/tools/plugins/com.google.dart.tools.core_test/src/com/google/dart/tools/core/internal/compiler/TestCompilerListener.java
diff --git a/editor/tools/plugins/com.google.dart.tools.core_test/src/com/google/dart/tools/core/internal/compiler/TestCompilerListener.java b/editor/tools/plugins/com.google.dart.tools.core_test/src/com/google/dart/tools/core/internal/compiler/TestCompilerListener.java
index f386c8912bdabb43c648d12f258cf5129faf17ad..5943a468c0f38f44135588b6b9edf4b597b111c7 100644
--- a/editor/tools/plugins/com.google.dart.tools.core_test/src/com/google/dart/tools/core/internal/compiler/TestCompilerListener.java
+++ b/editor/tools/plugins/com.google.dart.tools.core_test/src/com/google/dart/tools/core/internal/compiler/TestCompilerListener.java
@@ -13,17 +13,16 @@
  */
 package com.google.dart.tools.core.internal.compiler;
 
-import com.google.dart.compiler.DartCompilationError;
-import com.google.dart.compiler.DartCompilerListener;
-import com.google.dart.compiler.ast.DartUnit;
-
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
+import com.google.dart.compiler.DartCompilationError;
+import com.google.dart.compiler.DartCompilerListener;
+
 /**
  * A listener for validating that zero or more specific errors occurred during a compilation.
  */
-public class TestCompilerListener extends DartCompilerListener {
+public class TestCompilerListener extends DartCompilerListener.Empty {
   private String[] messages;
   private int[] line;
   private int[] column;
@@ -65,8 +64,4 @@ public class TestCompilerListener extends DartCompilerListener {
     assertEquals("Wrong column number", column[current], event.getColumnNumber());
     current++;
   }
-
-  @Override
-  public void unitCompiled(DartUnit unit) {
-  }
 }