This CL fixes weird performance implications when changing layout of Code::flags field:
it happened that the unused ICStateField with MONOMORPHIC value in the handlers' flags
was accidentally offsetting the underflow bug in stub cache probing code on arm, arm64,
mips and mips64.

Stub cache tests now work even when snapshot is enabled.

Drive-by-change: Fixed counters manipulation on arm64 and mips64.

BUG=chromium:618701

Review-Url: https://codereview.chromium.org/2161153002
Cr-Commit-Position: refs/heads/master@{#37910}