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 b4c628ebb297fa90d86594c2656423dada3dc298..27207975608eda4a0ed19b3646ee2d7c94a83e3b 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -773,8 +773,9 @@ 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(int* materialized_literal_count,
-                                      int* expected_property_count, bool* ok);
+  V8_INLINE void SkipLazyFunctionBody(
+      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);
@@ -1024,12 +1025,16 @@ 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(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(
@@ -1090,10 +1095,10 @@ const AstRawString* ParserTraits::EmptyIdentifierString() {
 
 
 void ParserTraits::SkipLazyFunctionBody(int* materialized_literal_count,
-                                        int* expected_property_count,
-                                        bool* ok) {
-  return parser_->SkipLazyFunctionBody(
-      materialized_literal_count, expected_property_count, ok);
+                                        int* expected_property_count, bool* ok,
+                                        Scanner::BookmarkScope* bookmark) {
+  return parser_->SkipLazyFunctionBody(materialized_literal_count,
+                                       expected_property_count, ok, bookmark);
 }