The ECMAScript ⊃ JSON proposal doesn’t affect LineContinuation
grammar. These tests verify that the behavior remains the same when
the --harmony-subsume-json feature flag is enabled.

Bug: v8:7418
Change-Id: Iec5cb1bc112f278481ba1202f0c2b8693917843a
Reviewed-on: https://chromium-review.googlesource.com/1067463Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Mathias Bynens <mathias@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53270}