Add counter to track Date::getTimezoneOffset().

Bug: chromium:915620
Change-Id: I75579080098632639b125b2252b3ab9615c7ea95
Reviewed-on: https://chromium-review.googlesource.com/c/1379876
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Mike West <mkwst@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58306}

include/v8.h

@@ -7427,6 +7427,7 @@ class V8_EXPORT Isolate {
     kOptimizedFunctionWithOneShotBytecode = 71,
     kRegExpMatchIsTrueishOnNonJSRegExp = 72,
     kRegExpMatchIsFalseishOnJSRegExp = 73,
+    kDateGetTimezoneOffset = 74,
 
     // If you add new values here, you'll also need to update Chromium's:
     // web_feature.mojom, UseCounterCallback.cpp, and enums.xml. V8 changes to

src/objects.cc

@@ -18677,6 +18677,7 @@ Object* JSDate::GetUTCField(FieldIndex index,
   int64_t time_ms = static_cast<int64_t>(value);
 
   if (index == kTimezoneOffset) {
+    GetIsolate()->CountUsage(v8::Isolate::kDateGetTimezoneOffset);
     return Smi::FromInt(date_cache->TimezoneOffset(time_ms));
   }