Reduce type-impedance for LayoutImageResource::GetImage

The container size will be converted to FloatSize in the end, so make
the argument type a FloatSize too rather than a LayoutSize.
Clean up callers, removing some conversions in SVGImagePainter, and add
an IntSize overload (since it's common to call GetImage with an
IntSize).

Change-Id: I4f5c4389d21617ad60d18b258674999e9ef51f2c
Reviewed-on: https://chromium-review.googlesource.com/c/1367651
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#615130}
7 files changed