Implement PersistentValueMap, a map that stores UniquePersistent values.
This is preparatory work to get rid of UnsafePersistent in blink.

The previous version had to be reverted due to timeouts in win32/Debug: https://codereview.chromium.org/197173002/

The timeouts happened because the STL version on that platform contains sanity checking code which opens a 'debug window' in the GUI, patiently waiting for the user to click ok/cancel/somethirdoption. It turns out, the cause for that debug window was totally valid and the test had a use-after-free issue.

The 1st patch set is the code as before. The 2nd patch set contains the fix.

Related blink changes are here: https://codereview.chromium.org/180363004/

This patch is largely based on https://codereview.chromium.org/175503003/, with some methods added to support the blink change mentioned above.

BUG=
R=dcarney@chromium.org

Review URL: https://codereview.chromium.org/197263002

Patch from Daniel Vogelheim <vogelheim@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19873 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix of argument materialization of captured heap numbers.

The escape analysis calculates the number of slots in an object as
no-of-slots = object-size / pointer-size.  This gives 3 slots for
heap numbers on 32-bit architectures (one slot for the map, two for
the double value); however, my argument materialization code assumed
just two slots (map + value). Since Hydrogen allocates heap numbers
quite rarely, it is hard to produce a more meaningful repro than the
one provided by Clusterfuzz. Any suggestions are welcome.

The fix is simple - we just read out all extra slots (beyond the map
and the double) for heap numbers.

R=mstarzinger@chromium.org
BUG=351315
LOG=N

Review URL: https://codereview.chromium.org/196283004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19874 ce2b1a6d-e550-0410-aec6-3dcde31c8c00