Revert r160169 "Handle the font size specified in a canvas when is in Rem format."

Introduces failing tests: http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&tests=canvas/philip/tests/2d.text.font.rem.html

BUG=

Review URL: https://codereview.chromium.org/35243002

git-svn-id: svn://svn.chromium.org/blink/trunk@160206 bbb929c8-8fbe-4397-9dbb-9b2b20218538