[parser] Only track parsing-mode (and possibly switch to the preparser) in the parser

src/parsing/parser.h

Index: src/parsing/parser.h
diff --git a/src/parsing/parser.h b/src/parsing/parser.h
index 00075f46e142303e0fc4c6cdfeda2d2d64ef90ad..19384f6fdba3581cc78d0c55a68ed2c1d5a98966 100644
--- a/src/parsing/parser.h
+++ b/src/parsing/parser.h
@@ -235,6 +235,22 @@ class V8_EXPORT_PRIVATE Parser : public NON_EXPORTED_BASE(ParserBase<Parser>) {
         original_scope_);
   }
 
+  bool parse_lazily() const { return mode_ == PARSE_LAZILY; }
+  enum Mode { PARSE_LAZILY, PARSE_EAGERLY };
+
+  class ParsingModeScope BASE_EMBEDDED {
+   public:
+    ParsingModeScope(Parser* parser, Mode mode)
+        : parser_(parser), old_mode_(parser->mode_) {
+      parser_->mode_ = mode;
+    }
+    ~ParsingModeScope() { parser_->mode_ = old_mode_; }
+
+   private:
+    Parser* parser_;
+    Mode old_mode_;
+  };
+
   // Runtime encoding of different completion modes.
   enum CompletionKind {
     kNormalCompletion,
@@ -1119,6 +1135,7 @@ class V8_EXPORT_PRIVATE Parser : public NON_EXPORTED_BASE(ParserBase<Parser>) {
   Scanner scanner_;
   PreParser* reusable_preparser_;
   Scope* original_scope_;  // for ES5 function declarations in sloppy eval
+  Mode mode_;
 
   friend class ParserTarget;
   friend class ParserTargetScope;