cc: Remove LayerTreeSettings::raster_enabled.
This was only used by tests to test using CC without a message
loop, however this isn't a mode that CC has to perform in
anymore now that WebView is using a cc::Display instead of a
full compositor as its parent compositor.
The setting caused the TileManager to be null sometimes, when it
wouldn't otherwise. Convert some of the if (tile_manager_) branches
to if (settings_.impl_side_painting) instead.
R=enne, vmpstr
BUG=413479
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
Review URL: https://codereview.chromium.org/
1179143004
Cr-Commit-Position: refs/heads/master@{#334485}