Create v8::HandleScope in JSBasedEventListener::GetSourceLocation()

This is the bug fixing for previous CL:
https://chromium-review.googlesource.com/c/chromium/src/+/1253317

v8::HandleScope was not named.

Bug: 894069
Change-Id: Ib9111275bad434b1968a4bd674a0b8932b8c1533
Reviewed-on: https://chromium-review.googlesource.com/c/1278548
Commit-Queue: Yuki Yamada <yukiy@google.com>
Reviewed-by: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599110}

third_party/blink/renderer/bindings/core/v8/js_based_event_listener.cc

@@ -161,7 +161,7 @@ void JSBasedEventListener::handleEvent(
 
 std::unique_ptr<SourceLocation> JSBasedEventListener::GetSourceLocation(
     EventTarget& target) {
-  v8::HandleScope(GetIsolate());
+  v8::HandleScope handle_scope(GetIsolate());
   v8::Local<v8::Value> effective_function = GetEffectiveFunction(target);
   if (effective_function->IsFunction())
     return SourceLocation::FromFunction(effective_function.As<v8::Function>());