Use DEFINE_STATIC_LOCAL for ParkableStringManager::instance

Change-Id: Ibb54621a413f1928a04498dae65a1ae5f3e48361
Reviewed-on: https://chromium-review.googlesource.com/1230716Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#592335}

third_party/blink/renderer/platform/bindings/parkable_string_manager.cc

@@ -20,7 +20,7 @@ namespace blink {
 
 ParkableStringManager& ParkableStringManager::Instance() {
   DCHECK(IsMainThread());
-  static ParkableStringManager instance;
+  DEFINE_STATIC_LOCAL(ParkableStringManager, instance, ());
   return instance;
 }