Add some support for promptly purging pages.

third_party/WebKit/Source/platform/heap/PagePool.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PagePool_h
 #define PagePool_h
 
 #include "platform/heap/ThreadState.h"
 #include "platform/wtf/Allocator.h"
 
 namespace blink {
 
 class PageMemory;
 
+enum class DecommitMemoryTiming { DecommitAsAppropriate, DecommitPromptly };
+
 // Once pages have been used for one type of thread heap they will never be
 // reused for another type of thread heap.  Instead of unmapping, we add the
 // pages to a pool of pages to be reused later by a thread heap of the same
 // type. This is done as a security feature to avoid type confusion.  The
 // heaps are type segregated by having separate thread arenas for different
 // types of objects.  Holding on to pages ensures that the same virtual address
 // space cannot be used for objects of another type than the type contained
 // in this page to begin with.
 class PagePool {
   USING_FAST_MALLOC(PagePool);
 
  public:
   PagePool();
   ~PagePool();
-  void Add(int, PageMemory*);
+
+  void Add(int,
+           PageMemory*,
+           DecommitMemoryTiming = DecommitMemoryTiming::DecommitAsAppropriate);
   PageMemory* Take(int);
 
  private:
   class PoolEntry {
     USING_FAST_MALLOC(PoolEntry);
 
    public:
     PoolEntry(PageMemory* data, PoolEntry* next) : data(data), next(next) {}
 
     PageMemory* data;
     PoolEntry* next;
   };
 
   PoolEntry* pool_[BlinkGC::kNumberOfArenas];
 };
 
 }  // namespace blink
 
 #endif