This CL also combines Runtime::GetGlobalInsideTypeof and Runtime::kGetGlobalNotInsideTypeof
to Runtime::GetGlobal with explicit typeof_mode parameter.

Drive-by-fix: tail call to correct Slow builtin from LoadCallback handlers when --runtime-call-stats is on.

BUG=chromium:576312

Review-Url: https://codereview.chromium.org/2144643004
Cr-Commit-Position: refs/heads/master@{#37710}