Add unitAboutToCompile() into DartCompilerListener

compiler/java/com/google/dart/compiler/DefaultDartCompilerListener.java

Index: compiler/java/com/google/dart/compiler/DefaultDartCompilerListener.java
diff --git a/compiler/java/com/google/dart/compiler/DefaultDartCompilerListener.java b/compiler/java/com/google/dart/compiler/DefaultDartCompilerListener.java
index 51a6739f2e91d9ea68588010cd5cdf1a2260cf73..7b7be62275a2649c105af78e9bd007c08b5f5ccf 100644
--- a/compiler/java/com/google/dart/compiler/DefaultDartCompilerListener.java
+++ b/compiler/java/com/google/dart/compiler/DefaultDartCompilerListener.java
@@ -13,7 +13,7 @@ import java.io.PrintStream;
  * A default implementation of {@link DartCompilerListener} which counts
  * compilation errors.
  */
-public class DefaultDartCompilerListener extends DartCompilerListener {
+public class DefaultDartCompilerListener implements DartCompilerListener {
 
   /**
    * The number of (fatal) problems that occurred during compilation.
@@ -47,18 +47,6 @@ public class DefaultDartCompilerListener extends DartCompilerListener {
     formatter = new  PrettyErrorFormatter(outputStream, useColor(), errorFormat);
   }
 
-  @Override
-  public void onError(DartCompilationError event) {
-    formatter.format(event);
-    if (event.getErrorCode().getSubSystem() == SubSystem.STATIC_TYPE) {
-      incrementTypeErrorCount();
-    } else if (event.getErrorCode().getErrorSeverity() == ErrorSeverity.ERROR) {
-      incrementErrorCount();
-    } else if (event.getErrorCode().getErrorSeverity() == ErrorSeverity.WARNING) {
-      incrementWarningCount();
-    }
-  }
-
   private boolean useColor() {
     return String.valueOf(System.getenv("TERM")).startsWith("xterm") && System.console() != null;
   }
@@ -112,6 +100,22 @@ public class DefaultDartCompilerListener extends DartCompilerListener {
   }
 
   @Override
+  public void onError(DartCompilationError event) {
+    formatter.format(event);
+    if (event.getErrorCode().getSubSystem() == SubSystem.STATIC_TYPE) {
+      incrementTypeErrorCount();
+    } else if (event.getErrorCode().getErrorSeverity() == ErrorSeverity.ERROR) {
+      incrementErrorCount();
+    } else if (event.getErrorCode().getErrorSeverity() == ErrorSeverity.WARNING) {
+      incrementWarningCount();
+    }
+  }
+
+  @Override
+  public void unitAboutToCompile(DartSource source, boolean diet) {
+  }
+
+  @Override
   public void unitCompiled(DartUnit unit) {
   }
 }