Oilpan: adjust GC policy under memory pressure (only.)

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 140fef86118bcbbdaadd7ba36a618be1ed3dd2c5..481455f76ba068a19a56142693ff03493579dffc 100644
--- a/Source/platform/heap/ThreadState.h
+++ b/Source/platform/heap/ThreadState.h
@@ -315,7 +315,7 @@ public:
     bool isMainThread() const { return this == mainThreadState(); }
     void checkThread() const { ASSERT(m_thread == currentThread()); }
 
-    void didV8GC();
+    void didV8MajorGC();
 
     void performIdleGC(double deadlineSeconds);
     void performIdleLazySweep(double deadlineSeconds);
@@ -652,13 +652,18 @@ private:
     // shouldSchedule{Precise,Idle}GC and shouldForceConservativeGC
     // implement the heuristics that are used to determine when to collect garbage.
     // If shouldForceConservativeGC returns true, we force the garbage
-    // collection immediately. Otherwise, if shouldGC returns true, we
+    // collection immediately. Otherwise, if should*GC returns true, we
     // record that we should garbage collect the next time we return
     // to the event loop. If both return false, we don't need to
     // collect garbage at this point.
     bool shouldScheduleIdleGC();
     bool shouldSchedulePreciseGC();
     bool shouldForceConservativeGC();
+
+    // Internal helper for GC policy handling code. Returns true if
+    // an urgent conservative GC is now needed due to memory pressure.
+    bool shouldForceMemoryPressureGC();
+
     void runScheduledGC(StackState);
 
     void eagerSweep();