Inline isUint32() method from HConstant, which was only used in one place.
Add utility method for checking whether an HValue is a given int32_t constant.

BUG=

Review URL: https://codereview.chromium.org/14244023

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14329 ce2b1a6d-e550-0410-aec6-3dcde31c8c00