Revert of Oilpan: Decommit backing storage of CallbackStacks

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

Index: third_party/WebKit/Source/platform/heap/CallbackStack.h
diff --git a/third_party/WebKit/Source/platform/heap/CallbackStack.h b/third_party/WebKit/Source/platform/heap/CallbackStack.h
index b961e91a6863005459710176537ac1cf949b0bae..0d60ebc3da73d0ae7f40f3fdca1ab4f4db56057d 100644
--- a/third_party/WebKit/Source/platform/heap/CallbackStack.h
+++ b/third_party/WebKit/Source/platform/heap/CallbackStack.h
@@ -41,7 +41,6 @@
     ~CallbackStack();
 
     void clear();
-    void decommit();
 
     Item* allocateEntry();
     Item* pop();
@@ -55,15 +54,25 @@
 #endif
 
 private:
-    static const size_t blockSize = (1 << 13);
+    static const size_t blockSize = 8192;
 
     class Block {
         USING_FAST_MALLOC(Block);
     public:
-        explicit Block(Block* next);
-        ~Block();
+        explicit Block(Block* next)
+            : m_limit(&(m_buffer[blockSize]))
+            , m_current(&(m_buffer[0]))
+            , m_next(next)
+        {
+            clearUnused();
+        }
 
-        void decommit();
+        ~Block()
+        {
+            clearUnused();
+        }
+
+        void clear();
 
         Block* next() const { return m_next; }
         void setNext(Block* next) { m_next = next; }
@@ -71,6 +80,11 @@
         bool isEmptyBlock() const
         {
             return m_current == &(m_buffer[0]);
+        }
+
+        size_t size() const
+        {
+            return blockSize - (m_limit - m_current);
         }
 
         Item* allocateEntry()
@@ -93,7 +107,9 @@
 #endif
 
     private:
-        Item* m_buffer;
+        void clearUnused();
+
+        Item m_buffer[blockSize];
         Item* m_limit;
         Item* m_current;
         Block* m_next;