Replace delete in favor of setting to undefined to prevent V8 deoptim…

…ization.

src/item/Item.js

@@ -214,10 +214,8 @@ var Item = Base.extend(Callback, /** @lends Item# */{
  project = this._project;
  if (flags & /*#=*/ ChangeFlag.GEOMETRY) {
  // Clear cached bounds and position whenever geometry changes
- delete this._bounds;
- delete this._position;
- delete this._decomposed;
- delete this._globalMatrix;
+ this._bounds = this._position = this._decomposed =
+ this._globalMatrix = undefined;
  }
  if (cacheParent && (flags
  & (/*#=*/ ChangeFlag.GEOMETRY | /*#=*/ ChangeFlag.STROKE))) {
@@ -814,7 +812,7 @@ var Item = Base.extend(Callback, /** @lends Item# */{
  setPivot: function(/* point */) {
  this._pivot = Point.read(arguments);
  // No need for _changed() since the only thing this affects is _position
- delete this._position;
+ this._position = undefined;
  },
 
  _pivot: null,
@@ -999,16 +997,15 @@ var Item = Base.extend(Callback, /** @lends Item# */{
  for (var i = 0, list = item._boundsCache.list, l = list.length;
  i < l; i++) {
  var child = list[i];
- delete child._bounds;
+ child._bounds = child._position = undefined;
  // Delete position as well, since it's depending on bounds.
- delete child._position;
  // We need to recursively call _clearBoundsCache, because if
  // the cache for this child's children is not valid anymore,
  // that propagates up the DOM tree.
  if (child !== item && child._boundsCache)
  child._clearBoundsCache();
  }
- delete item._boundsCache;
+ item._boundsCache = undefined;
  }
  }
  }