Previously, String.prototype.normalize constructed its ICU input
string as a null-terminated string. This creates a bug for strings
which contain a null byte, which is allowed in ECMAScript. This
patch constructs the ICU string based on its length so that the
entire string is normalized.

R=jshin@chromium.org
BUG=v8:4654
LOG=Y

Review URL: https://codereview.chromium.org/1645223003

Cr-Commit-Position: refs/heads/master@{#33614}