[oilpan]: optimize the way we allocate persistent handles in wrappers.

The oilpan JS wrappers all have a persistent which is used to keep the wrapped object around while there is a javascript reference to it. Allocation of these wrapper persistents showed up in some of benchmarks. This change creates a new optimized WrapperPersistent which is allocated in blocks. This gives a speedup ranging between a few percent to 20% in some of the more wrapper intensive tests.

R=ager@chromium.org, haraken@chromium.org, oilpan-reviews@chromium.org, zerny@chromium.org
BUG=

Review URL: https://codereview.chromium.org/525353002

git-svn-id: svn://svn.chromium.org/blink/trunk@181298 bbb929c8-8fbe-4397-9dbb-9b2b20218538