Add some support for promptly purging pages.

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

Index: third_party/WebKit/Source/platform/heap/PagePool.h
diff --git a/third_party/WebKit/Source/platform/heap/PagePool.h b/third_party/WebKit/Source/platform/heap/PagePool.h
index 082f83f15e8f265b6df080c280a3ae84df4a03f4..55620c07832da0d2ca6f6f853790d78a7858febe 100644
--- a/third_party/WebKit/Source/platform/heap/PagePool.h
+++ b/third_party/WebKit/Source/platform/heap/PagePool.h
@@ -12,6 +12,8 @@ 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
@@ -26,7 +28,10 @@ class PagePool {
  public:
   PagePool();
   ~PagePool();
-  void Add(int, PageMemory*);
+
+  void Add(int,
+           PageMemory*,
+           DecommitMemoryTiming = DecommitMemoryTiming::DecommitAsAppropriate);
   PageMemory* Take(int);
 
  private: