[strong] Fix inlining issue

[strong] Fix inlining issue

The Hydrogen representation for binops was never changed to care about the
language mode. We thought this was ok, but it turns out we need to keep track
of it to make sure inlining doesn't mess with the "strongness" of binops.

Also added more rigorous inlining testing.

BUG=v8:3956
LOG=N

Review URL: https://codereview.chromium.org/1123043002

Cr-Commit-Position: refs/heads/master@{#28253}