Oilpan: tweak heuristics for forcing conservative GC.

Source/platform/heap/ThreadState.h

Index: Source/platform/heap/ThreadState.h
diff --git a/Source/platform/heap/ThreadState.h b/Source/platform/heap/ThreadState.h
index 901ab8a7bf702d1cf4373d1c4c5860b8365ebd16..39df3f485979993816852eca748a5531967f905e 100644
--- a/Source/platform/heap/ThreadState.h
+++ b/Source/platform/heap/ThreadState.h
@@ -279,6 +279,8 @@ public:
     // collect garbage at this point.
     bool shouldGC();
     bool shouldForceConservativeGC();
+    bool increasedEnoughToGC(size_t, size_t);
+    bool increasedEnoughToForceConservativeGC(size_t, size_t);
 
     // If gcRequested returns true when a thread returns to its event
     // loop the thread will initiate a garbage collection.
@@ -544,6 +546,8 @@ private:
     void cleanup();
     void cleanupPages();
 
+    void setLowCollectionRate(bool value) { m_lowCollectionRate = value; }
+
     static WTF::ThreadSpecific<ThreadState*>* s_threadSpecific;
     static SafePointBarrier* s_safePointBarrier;
 
@@ -583,6 +587,8 @@ private:
     Vector<OwnPtr<CleanupTask> > m_cleanupTasks;
     bool m_isTerminating;
 
+    bool m_lowCollectionRate;
+
     CallbackStack* m_weakCallbackStack;
 
 #if defined(ADDRESS_SANITIZER)