WebGL TexParameterf and GetTexParameterf needs to handle float param correctly

Right now the param is always cast to int.

BUG=348810
TEST=ToT webgl conformance conformance/extensions/ext-texture-filter-anisotropic.html
R=kbr@chromium.org,bajones@chromium.org

Review URL: https://codereview.chromium.org/186733013

git-svn-id: svn://svn.chromium.org/blink/trunk@168771 bbb929c8-8fbe-4397-9dbb-9b2b20218538