Compare external pixel data length against Smi::kMaxValue

BUG=chromium:359802
LOG=n
R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/226133002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20519 ce2b1a6d-e550-0410-aec6-3dcde31c8c00