Implement a fast buffer allocator for Vector, HashTable and StringBuilder

Source/platform/heap/Heap.h

Index: Source/platform/heap/Heap.h
diff --git a/Source/platform/heap/Heap.h b/Source/platform/heap/Heap.h
index 6f2186551c63801842022a3cae9feb947b41ed40..4e1ca377b9e9adf0d9390c8f7d8d722e94db89b6 100644
--- a/Source/platform/heap/Heap.h
+++ b/Source/platform/heap/Heap.h
@@ -709,6 +709,7 @@ public:
 #endif
     Address lazySweep(size_t, size_t gcInfoIndex);
     void sweepUnsweptPage();
+    void freePage(BasePage*);
     // Returns true if we have swept all pages within the deadline.
     // Returns false otherwise.
     bool lazySweepWithDeadline(double deadlineSeconds);
@@ -717,6 +718,8 @@ public:
     ThreadState* threadState() { return m_threadState; }
     int heapIndex() const { return m_index; }
 
+    virtual void printStats() { }
+
 protected:
     BasePage* m_firstPage;
     BasePage* m_firstUnsweptPage;
@@ -760,6 +763,8 @@ public:
     bool shrinkObject(HeapObjectHeader*, size_t);
     void decreasePromptlyFreedSize(size_t size) { m_promptlyFreedSize -= size; }
 
+    void printStats() override;
+
 private:
     void allocatePage();
     Address lazySweepPages(size_t, size_t gcInfoIndex) override;
@@ -784,6 +789,15 @@ private:
     size_t m_allocationCount;
     size_t m_inlineAllocationCount;
 #endif
+
+    int m_promptlyFreeHit;
+    int m_promptlyFreeHitIgnored;
+    int m_promptlyFreeMiss;
+    int m_promptlyFreeMissIgnored;
+    int m_expandHit;
+    int m_expandHitIgnored;
+    int m_expandMiss;
+    int m_expandMissIgnored;
 };
 
 class LargeObjectHeap final : public BaseHeap {