Use GL_chromium_color_buffer_float extensions

New GL_chromium_color_buffer_float extensions will require that GPU
command buffer clients use sized internal formats if they wish to render
to floating point textures.

BUG=329605

Review URL: https://codereview.chromium.org/150083005

git-svn-id: svn://svn.chromium.org/blink/trunk@167013 bbb929c8-8fbe-4397-9dbb-9b2b20218538