[regexp] Undo removal of ParseRegExpSyntax

RegExpParser::ParseRegExpSyntax was added to allow the SpiderMonkey
embedding of irregexp to report early errors. It was removed in
https://chromium-review.googlesource.com/c/v8/v8/+/2509596 because it
was unused. This patch restores it, with a comment to prevent future
deletion.

Bug: v8:11368
Change-Id: Iebec7e14b92e9a0fccc08f2f1c85d8ff4d6173f1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2658037Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72453}

src/regexp/regexp-parser.cc

@@ -1829,6 +1829,15 @@ bool RegExpParser::ParseRegExp(Isolate* isolate, Zone* zone,
   return success;
 }
 
+bool RegExpParser::VerifyRegExpSyntax(Isolate* isolate, Zone* zone,
+                                      FlatStringReader* input,
+                                      JSRegExp::Flags flags,
+                                      RegExpCompileData* result,
+                                      const DisallowGarbageCollection& no_gc) {
+  RegExpParser parser(input, flags, isolate, zone);
+  return parser.Parse(result, no_gc);
+}
+
 RegExpBuilder::RegExpBuilder(Zone* zone, JSRegExp::Flags flags)
     : zone_(zone),
       pending_empty_(false),

src/regexp/regexp-parser.h

@@ -160,6 +160,12 @@ class V8_EXPORT_PRIVATE RegExpParser {
   static bool ParseRegExp(Isolate* isolate, Zone* zone, FlatStringReader* input,
                           JSRegExp::Flags flags, RegExpCompileData* result);
 
+  // Used by the SpiderMonkey embedding of irregexp.
+  static bool VerifyRegExpSyntax(Isolate* isolate, Zone* zone,
+                                 FlatStringReader* input, JSRegExp::Flags flags,
+                                 RegExpCompileData* result,
+                                 const DisallowGarbageCollection& nogc);
+
  private:
   bool Parse(RegExpCompileData* result, const DisallowGarbageCollection&);