CFI: fix invalid type cast from base class (Task) to a subclass (RenderTask), where the actual type is a subclass of TileTask.
CFI: fix invalid type cast from base class (Task) to a subclass (RenderTask),
where the actual type is a subclass of TileTask.

This bug has been found with the help of CFI (Control Flow Integrity) checker,
see https://sites.google.com/a/chromium.org/dev/developers/testing/control-flow-integrity

BUG=chromium:457523,chromium:513021
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1248923002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#340010}

Just-D/chromium-1,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,Just-D/chromium-1,Just-D/chromium-1,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Just-D/chromium-1,Pluto-tv/chromium-crosswalk,Chilledheart/chromium,Pluto-tv/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Chilledheart/chromium,Just-D/chromium-1,Just-D/chromium-1,Just-D/chromium-1,axinging/chromium-crosswalk,Pluto-tv/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Pluto-tv/chromium-crosswalk,Pluto-tv/chromium-crosswalk,Just-D/chromium-1,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Just-D/chromium-1