Add some support for promptly purging pages.

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

Index: third_party/WebKit/Source/platform/heap/HeapPage.h
diff --git a/third_party/WebKit/Source/platform/heap/HeapPage.h b/third_party/WebKit/Source/platform/heap/HeapPage.h
index 21158986d489ddafa800eec7fda910a8bf57832b..64a28a9fe5ae4b8a3715e9d1e1a37b20e2631b70 100644
--- a/third_party/WebKit/Source/platform/heap/HeapPage.h
+++ b/third_party/WebKit/Source/platform/heap/HeapPage.h
@@ -36,6 +36,7 @@
 #include "platform/PlatformExport.h"
 #include "platform/heap/BlinkGC.h"
 #include "platform/heap/GCInfo.h"
+#include "platform/heap/PagePool.h"
 #include "platform/heap/ThreadState.h"
 #include "platform/heap/Visitor.h"
 #include "platform/wtf/AddressSanitizer.h"
@@ -391,7 +392,8 @@ class BasePage {
   // following methods are not performance-sensitive.
   virtual size_t ObjectPayloadSizeForTesting() = 0;
   virtual bool IsEmpty() = 0;
-  virtual void RemoveFromHeap() = 0;
+  virtual void RemoveFromHeap(
+      DecommitMemoryTiming = DecommitMemoryTiming::DecommitAsAppropriate) = 0;
   virtual void Sweep() = 0;
   virtual void MakeConsistentForMutator() = 0;
   virtual void InvalidateObjectStartBitmap() = 0;
@@ -474,7 +476,8 @@ class NormalPage final : public BasePage {
 
   size_t ObjectPayloadSizeForTesting() override;
   bool IsEmpty() override;
-  void RemoveFromHeap() override;
+  void RemoveFromHeap(DecommitMemoryTiming =
+                          DecommitMemoryTiming::DecommitAsAppropriate) override;
   void Sweep() override;
   void MakeConsistentForMutator() override;
   void InvalidateObjectStartBitmap() override {
@@ -522,9 +525,14 @@ class NormalPage final : public BasePage {
     NormalPage* current_page_ = nullptr;
     // Offset into |m_currentPage| to the next free address.
     size_t allocation_point_ = 0;
+
+    void AddAvailable(BasePage*);
+    BasePage* TakeAvailable();
     // Chain of available pages to use for compaction. Page compaction picks the
     // next one when the current one is exhausted.
     BasePage* available_pages_ = nullptr;
+    BasePage* last_available_ = nullptr;
+
     // Chain of pages that have been compacted. Page compaction will add
     // compacted pages once the current one becomes exhausted.
     BasePage** compacted_pages_ = nullptr;
@@ -565,7 +573,8 @@ class LargeObjectPage final : public BasePage {
 
   size_t ObjectPayloadSizeForTesting() override;
   bool IsEmpty() override;
-  void RemoveFromHeap() override;
+  void RemoveFromHeap(DecommitMemoryTiming =
+                          DecommitMemoryTiming::DecommitAsAppropriate) override;
   void Sweep() override;
   void MakeConsistentForMutator() override;
   void InvalidateObjectStartBitmap() override {}
@@ -780,7 +789,7 @@ class PLATFORM_EXPORT NormalPageArena final : public BaseArena {
 
   Address AllocateObject(size_t allocation_size, size_t gc_info_index);
 
-  void FreePage(NormalPage*);
+  void FreePage(NormalPage*, DecommitMemoryTiming);
 
   bool Coalesce();
   void PromptlyFreeObject(HeapObjectHeader*);