New heap profiler: implement fast retaining sizes approximation.

src/utils.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 308 matching lines @@
 
   // Returns the pointer to the start of the data in the vector.
   T* start() const { return start_; }
 
   // Access individual vector elements - checks bounds in debug mode.
   T& operator[](int index) const {
     ASSERT(0 <= index && index < length_);
     return start_[index];
   }
 
+  T& at(int i) const { return operator[](i); }
+
   T& first() { return start_[0]; }
 
   T& last() { return start_[length_ - 1]; }
 
   // Returns a clone of this vector with a new backing store.
   Vector<T> Clone() const {
     T* result = NewArray<T>(length_);
     for (int i = 0; i < length_; i++) result[i] = start_[i];
     return Vector<T>(result, length_);
   }
@@ skipping 379 matching lines @@
 }
 
 template <class Dest, class Source>
 inline Dest BitCast(Source* source) {
   return BitCast<Dest>(reinterpret_cast<uintptr_t>(source));
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_UTILS_H_