Simple BlinkGC heap compaction.

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 a006d41adf842693779de4f04436644eacf6caf0..374827f5fb80c085df2c27a43ce3980432a57f4d 100644
--- a/third_party/WebKit/Source/platform/heap/HeapPage.h
+++ b/third_party/WebKit/Source/platform/heap/HeapPage.h
@@ -308,6 +308,9 @@ class FreeListEntry final : public HeapObjectHeader {
   FreeListEntry* next() const { return m_next; }
 
   NO_SANITIZE_ADDRESS
+  FreeListEntry** prevNext() { return &m_next; }
+
+  NO_SANITIZE_ADDRESS
   void append(FreeListEntry* next) {
     ASSERT(!m_next);
     m_next = next;
@@ -512,6 +515,8 @@ class NormalPage final : public BasePage {
 
   inline NormalPageArena* arenaForNormalPage() const;
 
+  size_t sweepAndCompact(NormalPage*&, size_t, BasePage**);
+
  private:
   HeapObjectHeader* findHeaderFromAddress(Address);
   void populateObjectStartBitMap();
@@ -665,6 +670,8 @@ class FreeList {
   // All FreeListEntries in the nth list have size >= 2^n.
   FreeListEntry* m_freeLists[blinkPageSizeLog2];
 
+  size_t freeListSize() const;
+
   friend class NormalPageArena;
 };
 
@@ -761,8 +768,15 @@ class PLATFORM_EXPORT NormalPageArena final : public BaseArena {
   bool isLazySweeping() const { return m_isLazySweeping; }
   void setIsLazySweeping(bool flag) { m_isLazySweeping = flag; }
 
+  size_t arenaSize();
+  size_t freeListSize();
+
+  void sweepAndCompact();
+
  private:
-  void allocatePage();
+  NormalPage* allocatePage();
+  void allocateAndAddPage();
+
   Address outOfLineAllocate(size_t allocationSize, size_t gcInfoIndex);
   Address allocateFromFreeList(size_t, size_t gcInfoIndex);