Check for cached transition to ExternalArray elements kind.

R=ishell@chromium.org, verwaest@chromium.org
BUG=v8:3337
LOG=Y

Review URL: https://codereview.chromium.org/291193011

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21466 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Fix representation inference for mutable double boxes.

R=jarin@chromium.org
BUG=v8:3307
TEST=mjsunit/regress/regress-3307
LOG=N

Review URL: https://codereview.chromium.org/298723014

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21467 ce2b1a6d-e550-0410-aec6-3dcde31c8c00