Implement a 'trial parse' step, that will abort pre-parsing excessively

src/parser.h

Index: src/parser.h
diff --git a/src/parser.h b/src/parser.h
index 8d557aed53eca468795303c536bbd17252890551..e99bbae9f58ea01ca87630114eb772cffc2905e2 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -756,9 +756,10 @@ class ParserTraits {
       bool name_is_strict_reserved, FunctionKind kind,
       int function_token_position, FunctionLiteral::FunctionType type,
       FunctionLiteral::ArityRestriction arity_restriction, bool* ok);
-  V8_INLINE void SkipLazyFunctionBody(const AstRawString* name,
-                                      int* materialized_literal_count,
-                                      int* expected_property_count, bool* ok);
+  V8_INLINE void SkipLazyFunctionBody(
+      const AstRawString* name, int* materialized_literal_count,
+      int* expected_property_count, bool* ok,
+      Scanner::BookmarkScope* bookmark = nullptr);
   V8_INLINE ZoneList<Statement*>* ParseEagerFunctionBody(
       const AstRawString* name, int pos, Variable* fvar,
       Token::Value fvar_init_op, FunctionKind kind, bool* ok);
@@ -1008,13 +1009,17 @@ class Parser : public ParserBase<ParserTraits> {
 
   // Skip over a lazy function, either using cached data if we have it, or
   // by parsing the function with PreParser. Consumes the ending }.
+  //
+  // If bookmark is set, the (pre-)parser may decide to abort skipping
+  // in order to force the function to be eagerly parsed, after all.
+  // In this case, it'll reset the scanner using the bookmark.
   void SkipLazyFunctionBody(const AstRawString* function_name,
                             int* materialized_literal_count,
-                            int* expected_property_count,
-                            bool* ok);
+                            int* expected_property_count, bool* ok,
+                            Scanner::BookmarkScope* bookmark = nullptr);
 
   PreParser::PreParseResult ParseLazyFunctionBodyWithPreParser(
-      SingletonLogger* logger);
+      SingletonLogger* logger, Scanner::BookmarkScope* bookmark = nullptr);
 
   // Consumes the ending }.
   ZoneList<Statement*>* ParseEagerFunctionBody(
@@ -1078,10 +1083,11 @@ const AstRawString* ParserTraits::EmptyIdentifierString() {
 
 void ParserTraits::SkipLazyFunctionBody(const AstRawString* function_name,
                                         int* materialized_literal_count,
-                                        int* expected_property_count,
-                                        bool* ok) {
-  return parser_->SkipLazyFunctionBody(
-      function_name, materialized_literal_count, expected_property_count, ok);
+                                        int* expected_property_count, bool* ok,
+                                        Scanner::BookmarkScope* bookmark) {
+  return parser_->SkipLazyFunctionBody(function_name,
+                                       materialized_literal_count,
+                                       expected_property_count, ok, bookmark);
 }