Avoid converting via or creating IntRect when we want a FloatRect

It's currently easy to use an IntRect when a FloatRect is needed
since there is an implicit (lossy) conversion from IntRect to
FloatRect. This patch changes some code to remove some
unnecessary conversions between the types.

(A float can store all integers up to, but not including,
16,777,217 so it the conversion is most of the time non-lossy)

R=fs@opera.com, pdr@chromium.org

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I324b79c3d78d387574f47a4bda8f7dc7bdad567b
Reviewed-on: https://chromium-review.googlesource.com/1124682
Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Fredrik Söderquist <fs@opera.com>
Commit-Queue: Daniel Bratell <bratell@opera.com>
Cr-Commit-Position: refs/heads/master@{#572306}
8 files changed