[parser] Lift template literal invalid escape restriction

src/parsing/parser.h

Index: src/parsing/parser.h
diff --git a/src/parsing/parser.h b/src/parsing/parser.h
index 7d2c9a30b4b98e2ceadd6ac42c4464f1a5c5aa88..4f7646c2ad34a4e118e228494ca43b5cc552c24d 100644
--- a/src/parsing/parser.h
+++ b/src/parsing/parser.h
@@ -586,7 +586,15 @@ class V8_EXPORT_PRIVATE Parser : public NON_EXPORTED_BASE(ParserBase<Parser>) {
   typedef TemplateLiteral* TemplateLiteralState;
 
   TemplateLiteralState OpenTemplateLiteral(int pos);
-  void AddTemplateSpan(TemplateLiteralState* state, bool tail);
+  // "should_cook" means that the span can be "cooked": in tagged template
+  // literals, both the raw and "cooked" representations are available to user
+  // code ("cooked" meaning that escape sequences are converted to their
+  // interpreted values). With the --harmony-template-escapes flag, invalid
+  // escape sequences cause the cooked span to be represented by undefined,
+  // instead of being a syntax error.
+  // "tail" indicates that this span is the last in the literal.
+  void AddTemplateSpan(TemplateLiteralState* state, bool should_cook,
+                       bool tail);
   void AddTemplateExpression(TemplateLiteralState* state,
                              Expression* expression);
   Expression* CloseTemplateLiteral(TemplateLiteralState* state, int start,