MIPS: Use Cells to check prototype chain validity (disabled by default).

MIPS: Use Cells to check prototype chain validity (disabled by default).

Original commit message:
The cells are stored as (hidden) properties on prototype objects. When a prototype object changes its map, then both its own validity cell and those of all "downstream" prototypes are invalidated; handlers for a given receiver embed the currently valid cell for that receiver's prototype during their compilation and check it on execution.

Other changes in this CL:
- Made Map::SetPrototype static (for GC safety of |this|).
- For prototype maps, keep track of the prototype object using them. This is required for being able to find and invalidate "downstream" prototypes' cells.
- Ensure that prototype maps are never shared, even if they are slow. This is required for the above.
- Minor "const" cleanup for a few Map field accessors.

BUG=

[paul.l..., 2015-04-14 17:03:18]

paul.lind@imgtec.com changed reviewers:
+ jkummerow@chromium.org, paul.lind@imgtec.com

[paul.l..., 2015-04-14 17:03:18]

l-g-t-m

However, like parent CL, it does not pass tests with flag on.

[paul.l..., 2015-04-15 01:59:48]

On 2015/04/14 17:03:18, paul.l... wrote:
> l-g-t-m
> 
> However, like parent CL, it does not pass tests with flag on.

Testing error on my part, the CL & its parent are fine.

[Jakob Kummerow, 2015-04-15 09:34:20]

On 2015/04/15 01:59:48, paul.l... wrote:
> On 2015/04/14 17:03:18, paul.l... wrote:
> > l-g-t-m
> > 
> > However, like parent CL, it does not pass tests with flag on.
> 
> Testing error on my part, the CL & its parent are fine.

Thanks for the port; I've merged it into the main CL.