Override fixed to float, generate code, enable tests.

BUG=angleproject:2405

Change-Id: Ic3e9a31eaf22372023b94081b0f4a83770dcabbe
Reviewed-on: https://chromium-review.googlesource.com/1144455
Commit-Queue: Frank Henigman <fjhenigman@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>