Avoid some unnecessary fast-properties map creations.

Avoid some unnecessary fast-properties map creations.

(1) When we have just normalized and re-fastified a map, we don't need to copy it again to set the is_prototype bit.
(2) When defining accessors causes a non-prototype object to go slow, don't force re-fastification.

BUG=v8:3267
LOG=n
R=verwaest@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=25221

[Jakob Kummerow, 2014-11-07 14:30:24]

jkummerow@chromium.org changed reviewers:
+ verwaest@chromium.org

[Toon Verwaest, 2014-11-07 14:31:31]

lgtm

[Jakob Kummerow, 2014-11-07 16:33:15]

Committed patchset #2 (id:20001) manually as 25221 (presubmit successful).