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This change reverts 7875d555.

Currently we only defer images for async decoding if they are on a tile
that is required for activation, which effectively means images coming
into the viewport from a compositor scroll would always be sync decoded.
Since this can lead to excessive checkerboarding in some cases,
eliminate this veto.

This veto condition was initially added to avoid overhead of creating
pending trees for pre-paint/pre-decode checker-imaged tiles. Follow up
changes should still attempt to minimize this overhead.

Also note that comparing the UMA data for
CheckerboardedNeedRasterContentArea for the CheckerImaging experiment on
canary, async decoding on the active tree shows an overall decrease in
checkerboarding. For a 28-day aggregation:

1) Async decoding without activation veto
0-1 pixels/frame : 99.608% for checkerimaging group compared with
99.567% for control.

2) Async decoding with activation veto
0-1 pixels/frame : 99.19% for checkerimaging group compared with
99.176% for control.

R=vmpstr@chromium.org

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I79aed0a7b3c4b14b50ff54c6237839c23d1ff5c1
Reviewed-on: https://chromium-review.googlesource.com/698875
Commit-Queue: Khushal <khushalsagar@chromium.org>
Reviewed-by: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506643}