cc: Remove unnecessary DCHECK and dead code from scheduler.
cc: Remove unnecessary DCHECK and dead code from scheduler.

This removes a DCHECK which fails in main frame before activation mode
and cleans some of the code in WillCommit. Some dead code around
forced redraw state is also removed.

R=enne@chromium.org
BUG=612596
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/1997473003
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#394874}

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