[iwyu] Add missing include

R=marja@chromium.org

Bug: v8:7965
Change-Id: Ifcdaaacebf846673b576e66a242efe727a7f3665
Reviewed-on: https://chromium-review.googlesource.com/c/1303716
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57070}

src/dateparser-inl.h

@@ -7,6 +7,7 @@
 
 #include "src/char-predicates-inl.h"
 #include "src/dateparser.h"
+#include "src/isolate.h"
 #include "src/unicode-cache-inl.h"
 
 namespace v8 {

tools/generate-header-include-checks.py

@@ -31,7 +31,6 @@ AUTO_EXCLUDE = [
   # blacklist of headers we need to fix (https://crbug.com/v8/7965).
   'src/compiler/js-context-specialization.h',
   'src/compiler/raw-machine-assembler.h',
-  'src/dateparser-inl.h',
   'src/regexp/jsregexp.h',
   'src/snapshot/object-deserializer.h',
   'src/transitions.h',