Remove ASSERT, this method can handle ExternalArrays just fine.
Remove ASSERT, this method can handle ExternalArrays just fine.

BUG=v8:4137
LOG=n
R=arv@chromium.org

Review URL: https://codereview.chromium.org/1179983002.

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#28970}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh