The previous JavaScript version created way too many ConsStrings for
longer strings, i.e. when using String.fromCharCode together with
Function.prototype.apply and arrays of char codes.

This version now always allocates sequential strings and therefore uses
way less memory when turning longer character sequences into strings,
and therefore fixes the memory regression on Google Maps.

BUG=chromium:609831
R=yangguo@chromium.org

Review-Url: https://codereview.chromium.org/2004733002
Cr-Commit-Position: refs/heads/master@{#36427}