Apply numeric casts correctly in typed arrays and related code.

R=jkummerow@chromium.org
BUG=353004
LOG=Y

Review URL: https://codereview.chromium.org/201873005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20020 ce2b1a6d-e550-0410-aec6-3dcde31c8c00