GCC: avoid template specialization in non namespace scope in blink::MemberBase

Fix this error in GCC compilation:
../../third_party/blink/renderer/platform/heap/member.h:251:13: error: explicit specialization in non-namespace scope ‘class blink::MemberBase<T, tracenessConfiguration>’
  251 |   template <>
      |             ^
../../third_party/blink/renderer/platform/heap/member.h:252:76: error: template-id ‘SetRaw<blink::TracenessMemberConfiguration::kUntraced>’ in declaration of primary template
  252 |   ALWAYS_INLINE void SetRaw<TracenessMemberConfiguration::kUntraced>(T* raw) {

To avoid it we change SetRaw to not be a template method, and just check
the traceness configuration. The generated code should be the same.

Bug: 819294
Change-Id: Ia03d7842918bd091beaf966caa3af5e8c647cd76
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2360020Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: José Dapena Paz <jdapena@igalia.com>
Cr-Commit-Position: refs/heads/master@{#800153}

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

@@ -244,13 +244,11 @@ 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;
+    if (tracenessConfiguration == TracenessMemberConfiguration::kUntraced)
+      raw_ = raw;
+    else
+      WTF::AsAtomicPtr(&raw_)->store(raw, std::memory_order_relaxed);
   }
   ALWAYS_INLINE T* GetRaw() const { return raw_; }