Paint local background colors onto foreground layer.
This patch adds support for drawing backgrounds into the scrolling content
layer. This allows us to render text with sub-pixel anti-aliasing when an
opaque background color is used meaning that we can now promote in these
cases, and correctly supports content-box clips on locally attached
backgrounds (see overflow-scroll-with-local-background.html test).
BUG=381840
TEST=compositing/overflow/overflow-scroll-with-local-background.html,compositing/overflow/overflow-scroll-with-transparent-background.html,compositing/overflow/overflow-scroll-with-opaque-background.html
Review-Url: https://codereview.chromium.org/2196583002
Cr-Commit-Position: refs/heads/master@{#410797}
16 files changed
