Retrieve the native context/global object from the Node being
specialized in the JSNativeContextSpecialization and the
JSGlobalObjectSpecialization classes. For this we introduce two
new methods NodeProperties::GetSpecializationNativeContext and
NodeProperties::GetSpecializationGlobalObject, which walk up
the context chain and might in the end take the native context
from the outermost activation (if native context specialization
is enabled). This allows us to run the native context specialization
pass as part of the inlining phase without hacking some of that into
the JSInliner.

Also refactor the NodeProperties::GetSpecializationContext method
that was previously local to the JSContextSpecialization.

Also refactor two other oddities in JSNativeContextSpecialization.

R=jarin@chromium.org
BUG=v8:4470, v8:4493
LOG=n

Review URL: https://codereview.chromium.org/1451143005

Cr-Commit-Position: refs/heads/master@{#32076}