Oilpan: simplify away StoppingOtherThreads pseudo GCState.

Source/platform/heap/SafePoint.h

Index: Source/platform/heap/SafePoint.h
diff --git a/Source/platform/heap/SafePoint.h b/Source/platform/heap/SafePoint.h
index 76713c4c9cf6fcf91b7bcb568bfadc520a6580ea..29d248a99d65534a27f80f70259a098e646e8be6 100644
--- a/Source/platform/heap/SafePoint.h
+++ b/Source/platform/heap/SafePoint.h
@@ -13,8 +13,8 @@ namespace blink {
 class SafePointScope final {
     WTF_MAKE_NONCOPYABLE(SafePointScope);
 public:
-    explicit SafePointScope(ThreadState::StackState stackState)
-        : m_state(ThreadState::current())
+    SafePointScope(ThreadState::StackState stackState, ThreadState* state = ThreadState::current())
+        : m_state(state)
     {
         RELEASE_ASSERT(!m_state->isAtSafePoint());
         m_state->enterSafePoint(stackState, this);
@@ -22,8 +22,7 @@ public:
 
     ~SafePointScope()
     {
-        if (m_state)
-            m_state->leaveSafePoint();
+        m_state->leaveSafePoint();
     }
 
 private: