For strict equality `a === b` with Symbol feedback we need to check only
one side via CheckSymbol, since the resulting comparison can only be
true if both sides are symbols. For consistency with the receivers case
we check the left side, so CheckSymbol(a). This significantly reduces
the number of CheckSymbol operations in optimized code for the ARES-6
Air benchmark.

Bug: v8:6344
Change-Id: I50420f8d862fec31214b7e86b17919edcfc1f23e
Reviewed-on: https://chromium-review.googlesource.com/1213173
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55731}