Avoid data races on initializing GCScope.

third_party/WebKit/Source/platform/heap/SafePoint.h

Index: third_party/WebKit/Source/platform/heap/SafePoint.h
diff --git a/third_party/WebKit/Source/platform/heap/SafePoint.h b/third_party/WebKit/Source/platform/heap/SafePoint.h
index 0b96633b51b4b40dcd08a8fa33228eb410f5901a..f312ea612b8c719bd1960a3546091ff7021b07a7 100644
--- a/third_party/WebKit/Source/platform/heap/SafePoint.h
+++ b/third_party/WebKit/Source/platform/heap/SafePoint.h
@@ -13,13 +13,12 @@ namespace blink {
 class SafePointScope final {
     WTF_MAKE_NONCOPYABLE(SafePointScope);
 public:
-    explicit SafePointScope(BlinkGC::StackState stackState, ThreadState* state = ThreadState::current())
+    explicit SafePointScope(BlinkGC::StackState stackState, ThreadState* state = ThreadState::current(), bool delayEnter = false)
         : m_state(state)
     {
-        if (m_state) {
-            RELEASE_ASSERT(!m_state->isAtSafePoint());
-            m_state->enterSafePoint(stackState, this);
-        }
+        if (delayEnter)
+            return;
+        enter(stackState);
     }
 
     ~SafePointScope()
@@ -28,6 +27,15 @@ public:
             m_state->leaveSafePoint();
     }
 
+    void enter(BlinkGC::StackState stackState)
+    {
+        if (!m_state)
+            return;
+
+        RELEASE_ASSERT(!m_state->isAtSafePoint());
+        m_state->enterSafePoint(stackState, this);
+    }
+
 private:
     ThreadState* m_state;
 };