This clears the context register by setting it to Smi(0) before calling
the Runtime::kNotifyDeoptimized helper. The deoptimizer must be able to
materialize all heap objects without any context available. The context
itself might be dematerialized.

With this change we make sure that invariant is maintained even without
escape analysis kicking in. We also satisfy the check that the context
register is either Smi(0) or a valid context. It might have been the
special {arguments_marker} in this particular case.

R=bmeurer@chromium.org
BUG=chromium:644245

Review-Url: https://codereview.chromium.org/2320673002
Cr-Commit-Position: refs/heads/master@{#39267}