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..7222fe4e58fabc882aa263bf8d835b8b6c258c40 100644
--- a/Source/platform/heap/SafePoint.h
+++ b/Source/platform/heap/SafePoint.h
@@ -13,11 +13,13 @@ 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())

[haraken, 2015/05/31 00:13:20]

This looks a bit messy though -- sometimes take an optional parameter, sometimes
take nullptr which is actually a flag to change the behavior.

I'd prefer calling enter/leaveSafePoint() in GCScope's constructor/destructor to
avoid the mess.

[sof, 2015/05/31 10:28:09]

If you explicitly supply no ThreadState, it just behaves accordingly. Depending
on upstream changes, we may be able to avoid supporting a nullable ThreadState.

The constructor still needs an 'explicit' - added back.

+        : m_state(state)
     {
-        RELEASE_ASSERT(!m_state->isAtSafePoint());
-        m_state->enterSafePoint(stackState, this);
+        if (m_state) {
+            RELEASE_ASSERT(!m_state->isAtSafePoint());
+            m_state->enterSafePoint(stackState, this);
+        }
     }
 
     ~SafePointScope()