The new approach is that instead of compiling custom handlers for
every global object's PropertyCell it uses single dispatcher that
caches PropertyCells in respective slot of the feedback vector.

Currently the new LoadGlobalIC machinery is disabled.

This CL also removes unused LoadGlobalViaContext* stuff.

BUG=chromium:576312
LOG=Y

Review-Url: https://codereview.chromium.org/2065113002
Cr-Commit-Position: refs/heads/master@{#37002}