Update semantic highlighting only if there are no parse errors

compiler/java/com/google/dart/compiler/ast/DartUnit.java

Index: compiler/java/com/google/dart/compiler/ast/DartUnit.java
diff --git a/compiler/java/com/google/dart/compiler/ast/DartUnit.java b/compiler/java/com/google/dart/compiler/ast/DartUnit.java
index 15c2537b2bd0093a75c00a5211418c35c4cc6624..063455ee721c8a9dfd0e50775633492fa3e510d9 100644
--- a/compiler/java/com/google/dart/compiler/ast/DartUnit.java
+++ b/compiler/java/com/google/dart/compiler/ast/DartUnit.java
@@ -24,6 +24,8 @@ public class DartUnit extends DartNode {
   private final NodeList<DartComment> comments = NodeList.create(this);
   private final DartSource source;
   private final boolean isDiet;
+  
+  private boolean hasParseErrors;
 
   public DartUnit(DartSource source, boolean isDiet) {
     this.source = source;
@@ -69,6 +71,14 @@ public class DartUnit extends DartNode {
     return isDiet;
   }
 
+  public void setHasParseErrors(boolean hasParseErrors) {
+    this.hasParseErrors = hasParseErrors;
+  }
+  
+  public boolean hasParseErrors() {
+    return hasParseErrors;
+  }
+
   /**
    * Answer the receiver's directives, not <code>null</code>.
    */