Clang warn implicit float to int conversion 1. add '-Wfloat-conversion' in compiler flag for clang 2. fix existed implicit float conversion Bug: angleproject:3728 Change-Id: I0dc07eeb74c5d6dc480c6f0aa88bc75ab98e4292 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1713741 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>