Nested arrow functions can have the same end positions, so
the end position is unsuitable to decide whether a scope is
an inner function scope.

BUG=chromium:696202
R=jgruber@chromium.org, kozyatinskiy@chromium.org

Review-Url: https://codereview.chromium.org/2751573003
Cr-Commit-Position: refs/heads/master@{#43797}