Merged r14469 into trunk branch.

MIPS: HasOnlyAsciiChars can return incorrect results. Fixup usages and rename.

R=jkummerow@chromium.org
BUG=

Review URL: https://codereview.chromium.org/14021005

git-svn-id: https://v8.googlecode.com/svn/trunk@14471 ce2b1a6d-e550-0410-aec6-3dcde31c8c00