Use the PaintImage::GetSupportedDecodeSize API in the
SoftwareImageDecodeCache to decode directly to the scaled size, instead
of decoding to the original size and scaling.

R=ericrk@chromium.org

Bug: 558070,761564
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ia2e71961acad9f40648212f8be5fef734fea9fe3
Reviewed-on: https://chromium-review.googlesource.com/1106608Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Eric Karl <ericrk@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569321}