Introduce a new JSGlobalSpecialization advanced reducer that runs
during the initial inlining and context specialization, and specializes
the graph to the globals of the native context.  Currently we assume
that we do not inline cross native context, but long-term we will grab
the global object from the JSLoadGlobal/JSStoreGlobal feedback (with the
new global load/store ICs that are currently in the workings), and then
this whole specialization will be fully compositional even across
cross-context inlining.

Note that we cannot really handle most of the stores to global object
property cells because TurboFan doesn't have a mechanism to enforce
certain representations.  Also note that we cannot yet fully benefit
from the type feedback collected on the global object property cells,
because the type system cannot deal with maps in a reasonable way.

CQ_INCLUDE_TRYBOTS=tryserver.v8:v8_linux_nosnap_rel
R=jarin@chromium.org
BUG=v8:4470
LOG=n

Committed: https://crrev.com/6fbf7903f94924ea066af481719898bd9667b6eb
Cr-Commit-Position: refs/heads/master@{#31139}

Review URL: https://codereview.chromium.org/1387393002

Cr-Commit-Position: refs/heads/master@{#31148}