Now LookupIterator follows the same pattern of prepare transition, apply transition
and write value when adding new properties to dictionary objects.

JSGlobalObject case:
* Prepare transition phase ensures that there is a "transition" property cell
  prepared for receiving a value.
* Apply transition phase does nothing.
* Prepare for data property phase ensures that the existing property cell can
  receive the value.
* Write value phase writes value directly to the current property cell.

JSObject case:
* Prepare transition phase prepares the object for receiving a data value (which
  could switch an object to dictionary mode).
* Apply transition phase migrates object to a transition map. If the map happened
  to be a dictionary mode object's map then an uninitialized entry added to the
  properties dictionary.
* Prepare for data property phase does nothing.
* Write value phase just puts value to the properties dictionary.

BUG=chromium:576312

Review-Url: https://codereview.chromium.org/2127583002
Cr-Commit-Position: refs/heads/master@{#37585}