Simplify BackgroundImageGeometry by removing meaningless distinctions.

Simplify BackgroundImageGeometry by removing meaningless distinctions.

m_destOrigin is only set at the very end of
BoxPainter::calculateBackgroundImageGeometry, and then always to
destRect().location(). m_destRect is not changed after this point.

m_destOrigin is only read in relativePhase(), which is only called after the
end of calculateBackgroundGeometry.

As a result, relativePhase() always returns m_phase, and we should be able to
safely remove both relativePhase and destOrigin. It's not entirely clear to me
what these were supposed to do, but at the moment they do nothing.

TEST=LayoutTests

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=183771

[jbroman, 2014-10-15 19:31:24]

jbroman@chromium.org changed reviewers:
+ eae@chromium.org, pdr@chromium.org

[jbroman, 2014-10-15 19:32:18]

jbroman@chromium.org changed reviewers:
+ chrishtr@chromium.org, fmalita@chromium.org

[jbroman, 2014-10-15 19:32:19]

I couldn't find any distinction here while trying to understand this code, and
the layout tests seem to pass. PTAL.

[pdr., 2014-10-15 22:49:59]

The CQ bit was checked by pdr@chromium.org

[pdr., 2014-10-15 22:50:00]

LGTM

[commit-bot: I haz the power, 2014-10-15 22:50:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/660523003/1

[commit-bot: I haz the power, 2014-10-15 22:54:49]

Committed patchset #1 (id:1) as 183771