heap: Optimize writes to UntracedMember

Bug: 1030176
Change-Id: Ib820033632bbf107bf33710eadc343a7c48d5cd6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2352929Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797343}

third_party/blink/renderer/platform/heap/member.h

@@ -244,9 +244,14 @@ class MemberBase {
 #endif  // DCHECK_IS_ON()
   }
 
+  template <TracenessMemberConfiguration = tracenessConfiguration>
   ALWAYS_INLINE void SetRaw(T* raw) {
     WTF::AsAtomicPtr(&raw_)->store(raw, std::memory_order_relaxed);
   }
+  template <>
+  ALWAYS_INLINE void SetRaw<TracenessMemberConfiguration::kUntraced>(T* raw) {
+    raw_ = raw;
+  }
   ALWAYS_INLINE T* GetRaw() const { return raw_; }
 
  private: