Drop FilterEffect::m_absolutePaintRect

This rect is a remnant of the old ImageBuffer-based implementation of
FilterEffect, and is likely doing more harm than good at this point in
time. If we want to cache the result of a call to
determineAbsolutePaintRect(), that can be done equally well by the
client code.

Since removing this state removes the last side-effect from the
determineAbsolutePaintRect() methods we can mark it and related methods
(affectsTransparentPixels) as const.

BUG=642035

Review-Url: https://codereview.chromium.org/2329803002
Cr-Commit-Position: refs/heads/master@{#417908}
19 files changed