Add unitAboutToCompile() into DartCompilerListener

editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/utilities/compiler/DartCompilerUtilities.java

Index: editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/utilities/compiler/DartCompilerUtilities.java
diff --git a/editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/utilities/compiler/DartCompilerUtilities.java b/editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/utilities/compiler/DartCompilerUtilities.java
index 34b7dabf241600123b53f6a6c642c81bd6dd452b..34d2dd4d9958cafc6f40238a3bb939a629577c28 100644
--- a/editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/utilities/compiler/DartCompilerUtilities.java
+++ b/editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/utilities/compiler/DartCompilerUtilities.java
@@ -71,7 +71,7 @@ public class DartCompilerUtilities {
    * The abstract class <code>CompilerRunner</code> defines behavior common to classes used to
    * safely invoke the parser, record compilation errors, and capture any parser exception.
    */
-  private static abstract class CompilerRunner extends DartCompilerListener {
+  private static abstract class CompilerRunner implements DartCompilerListener {
     private final Collection<DartCompilationError> parseErrors;
     protected Throwable exception;
 
@@ -106,6 +106,10 @@ public class DartCompilerUtilities {
     }
 
     @Override
+    public void unitAboutToCompile(DartSource source, boolean diet) {
+    }
+
+    @Override
     public void unitCompiled(DartUnit unit) {
     }