https://codereview.chromium.org/1343113003 introduced a separate InternalPackedArray constructor to the extras utils object, distinct from the one used by natives. However, it omitted the code to set up the methods for that InternalPackedArray. This makes all the basic manipulation methods available.

BUG=v8:4276
LOG=Y
R=jochen@chromium.org,yangguo@chromium.org

Review URL: https://codereview.chromium.org/1401243003

Cr-Commit-Position: refs/heads/master@{#31272}