Implement tracking and optimizations of packed arrays

src/elements.h

Index: src/elements.h
diff --git a/src/elements.h b/src/elements.h
index 55d6fa56f0f3e23549909bcdc65a380f1f025e11..822fca50eee58def6ef88b2299c4774a99e16258 100644
--- a/src/elements.h
+++ b/src/elements.h
@@ -28,6 +28,7 @@
 #ifndef V8_ELEMENTS_H_
 #define V8_ELEMENTS_H_
 
+#include "elements-kind.h"
 #include "objects.h"
 #include "heap.h"
 #include "isolate.h"
@@ -45,6 +46,10 @@ class ElementsAccessor {
   virtual ElementsKind kind() const = 0;
   const char* name() const { return name_; }
 
+  // Checks the elements of an object for consistency, asserting when a problem
+  // is found.
+  virtual void Validate(JSObject* obj) = 0;
+
   // Returns true if a holder contains an element with the specified key
   // without iterating up the prototype chain.  The caller can optionally pass
   // in the backing store to use for the check, which must be compatible with