Oilpan: adjust GC policy under memory pressure.

Source/platform/heap/ThreadState.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 301 matching lines @@
         return reinterpret_cast<ThreadState*>(s_mainThreadStateStorage);
     }
 
     bool isMainThread() const { return this == mainThreadState(); }
     bool checkThread() const
     {
         ASSERT(m_thread == currentThread());
         return true;
     }
 
-    void didV8GC();
+    void didV8MajorGC(bool forceGC);
 
     void performIdleGC(double deadlineSeconds);
     void performIdleLazySweep(double deadlineSeconds);
 
     void scheduleIdleGC();
     void scheduleIdleLazySweep();
     void schedulePreciseGC();
     void scheduleGCIfNeeded();
     void setGCState(GCState);
     GCState gcState() const;
@@ skipping 316 matching lines @@
     NO_SANITIZE_ADDRESS void copyStackUntilSafePointScope();
     void clearSafePointScopeMarker()
     {
         m_safePointStackCopy.clear();
         m_safePointScopeMarker = nullptr;
     }
 
     // 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 shouldForceConservativeGC() and didV8MajorGC();
+    // returns true iff an urgent conservative GC is needed to try to
+    // relieve memory pressure.
+    bool shouldForceMemoryPressureGC();
+
     void runScheduledGC(StackState);
 
     void eagerSweep();
 
 #if defined(ADDRESS_SANITIZER)
     void poisonEagerHeap(Poisoning);
     void poisonAllHeaps();
 #endif
 
     // When ThreadState is detaching from non-main thread its
@@ skipping 95 matching lines @@
 };
 
 template<> class ThreadStateFor<AnyThread> {
 public:
     static ThreadState* state() { return ThreadState::current(); }
 };
 
 } // namespace blink
 
 #endif // ThreadState_h