Check if ArrayBuffer allocation in ArrayBufferBuilder is successful.

ArrayBuffer::create may return NULL if allocation fails.

BUG=353966

Review URL: https://codereview.chromium.org/206243002

git-svn-id: svn://svn.chromium.org/blink/trunk@169680 bbb929c8-8fbe-4397-9dbb-9b2b20218538