Speed up parsing w/ grammar shortcut.

src/parsing/preparser.h

Index: src/parsing/preparser.h
diff --git a/src/parsing/preparser.h b/src/parsing/preparser.h
index 280f1df5f855c4e096b926a342c1d71d43072367..ca5c182c685c7a506087553878261a50808512af 100644
--- a/src/parsing/preparser.h
+++ b/src/parsing/preparser.h
@@ -200,10 +200,20 @@ class PreParserExpression {
         ExpressionTypeField::encode(kNoTemplateTagExpression));
   }
 
+  static PreParserExpression Empty() {
+    return PreParserExpression(TypeField::encode(kExpression) |
+                               ExpressionTypeField::encode(kEmptyExpression));
+  }
+
   bool IsIdentifier() const {
     return TypeField::decode(code_) == kIdentifierExpression;
   }
 
+  bool IsEmptyExpression() const {
+    return TypeField::decode(code_) == kExpression &&
+           ExpressionTypeField::decode(code_) == kEmptyExpression;
+  }
+
   PreParserIdentifier AsIdentifier() const {
     DCHECK(IsIdentifier());
     return PreParserIdentifier(IdentifierTypeField::decode(code_));
@@ -316,7 +326,8 @@ class PreParserExpression {
     kCallEvalExpression,
     kSuperCallReference,
     kNoTemplateTagExpression,
-    kAssignment
+    kAssignment,
+    kEmptyExpression
   };
 
   explicit PreParserExpression(uint32_t expression_code)
@@ -334,7 +345,7 @@ class PreParserExpression {
 
   // The rest of the bits are interpreted depending on the value
   // of the Type field, so they can share the storage.
-  typedef BitField<ExpressionType, TypeField::kNext, 3> ExpressionTypeField;
+  typedef BitField<ExpressionType, TypeField::kNext, 4> ExpressionTypeField;
   typedef BitField<bool, TypeField::kNext, 1> IsUseStrictField;
   typedef BitField<PreParserIdentifier::Type, TypeField::kNext, 10>
       IdentifierTypeField;
@@ -662,6 +673,10 @@ class PreParserTraits {
     return expression.IsIdentifier();
   }
 
+  static bool IsEmptyExpression(PreParserExpression expression) {
+    return expression.IsEmptyExpression();
+  }
+
   static PreParserIdentifier AsIdentifier(PreParserExpression expression) {
     return expression.AsIdentifier();
   }
@@ -772,7 +787,7 @@ class PreParserTraits {
     return PreParserIdentifier::Default();
   }
   static PreParserExpression EmptyExpression() {
-    return PreParserExpression::Default();
+    return PreParserExpression::Empty();
   }
   static PreParserExpression EmptyLiteral() {
     return PreParserExpression::Default();