Reverting a performance optimization - I'm not comfortable it's side-effect free.

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

Index: compiler/java/com/google/dart/compiler/ast/DartNode.java
===================================================================
--- compiler/java/com/google/dart/compiler/ast/DartNode.java	(revision 14418)
+++ compiler/java/com/google/dart/compiler/ast/DartNode.java	(working copy)
@@ -117,10 +117,7 @@
    * @param visitor the visitor that will be used to visit the child
    */
   protected void safelyVisitChild(DartNode child, ASTVisitor<?> visitor) {
-    // Inline the DartIdentifier path - it's by far the most common.
-    if (child instanceof DartIdentifier) {
-      visitor.visitIdentifier((DartIdentifier)child);
-    } else if (child != null) {
+    if (child != null) {
       child.accept(visitor);
     }
   }