Use float comparison macros in caching entropy test.

BUG=342515
TEST=Tests stop failing on precise official builders.

Review URL: https://codereview.chromium.org/150833005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250643 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250643