Eliminate some virtual function from AST classes.

src/ast.cc

Index: src/ast.cc
===================================================================
--- src/ast.cc	(revision 9837)
+++ src/ast.cc	(working copy)
@@ -48,19 +48,22 @@
 // ----------------------------------------------------------------------------
 // Implementation of other node functionality.
 
-Assignment* ExpressionStatement::StatementAsSimpleAssignment() {
-  return (expression()->AsAssignment() != NULL &&
-          !expression()->AsAssignment()->is_compound())
-      ? expression()->AsAssignment()
-      : NULL;
+
+bool Expression::IsSmiLiteral() {
+  return AsLiteral() != NULL && AsLiteral()->handle()->IsSmi();
 }
 
 
-CountOperation* ExpressionStatement::StatementAsCountOperation() {
-  return expression()->AsCountOperation();
+bool Expression::IsStringLiteral() {
+  return AsLiteral() != NULL && AsLiteral()->handle()->IsString();
 }
 
 
+bool Expression::IsNullLiteral() {
+  return AsLiteral() != NULL && AsLiteral()->handle()->IsNull();
+}
+
+
 VariableProxy::VariableProxy(Isolate* isolate, Variable* var)
     : Expression(isolate),
       name_(var->name()),