The number of inobject properties used to be derived from the number
of this property assignments in the constructor (and increased by 2 to
allow for properties added later). This very often leads to wasted inobject 
slots.

This patch reclaims some of the unused inobject space by the following method:
 - for each constructor function the first several objects are allocated using the initial 
   ("generous) instance size estimation (this is called 'tracking phase').
 - during the tracking phase map transitions are tracked and actual property counts are collected.
 - at the end of the tracking phase instance sizes in the maps are decreased if necessary
   (starting with the function's initial map and traversing the transition tree).
 - all further allocation use more realistic instance size estimation.

Shrinking generously allocated objects without costly heap traversal is made possible 
by initializing their inobject properties with one_pointer_filler_map (instead of undefined). 

The initial slack for the generous allocation is increased from 2 to 6 which really helps some tests.

Review URL: http://codereview.chromium.org/3329019

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@5510 ce2b1a6d-e550-0410-aec6-3dcde31c8c00