Unify code paths for fixed and absolutely positioned objects in accumulateOffsetTowardsAncestor().

Unify code paths for fixed and absolutely positioned objects in accumulateOffsetTowardsAncestor().

Deleted most of the code specific to handling of fixed-positioned objects, and
have fixed-positioned objects use the code for absolutely positioned objects
instead. One piece needs to be kept, though: If the container of a fixed
positioned object is the viewport, we need to make sure that we call
LayoutObject::localToAbsolute() to calculate the correct position, since
DeprecatedPaintLayer::location() doesn't handle fixed-positioning properly.

This gets rid of an assertion failure that would trigger when we had a multicol
with a transform with a fixedpos.

BUG=496929
R=chrishtr@chromium.org,jchaffraix@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=199725

[mstensho (USE GERRIT), 2015-07-29 19:11:25]

Just couldn't figure out why we would need (let alone want) separate code paths
for fixed positioneds and absolutely positioneds. And since unifying them didn't
break any tests, I guess we're good to go?

[Julien - ping for review, 2015-07-29 23:10:52]

lgtm

Yay to unifying!

https://codereview.chromium.org/1268493002/diff/1/LayoutTests/fast/multicol/t...
File LayoutTests/fast/multicol/transform-with-fixedpos-crash.html (right):

https://codereview.chromium.org/1268493002/diff/1/LayoutTests/fast/multicol/t...
LayoutTests/fast/multicol/transform-with-fixedpos-crash.html:6: <p>PASS if no
crash or assertion failure.</p>
Let's add a description of what is tested.

https://codereview.chromium.org/1268493002/diff/1/LayoutTests/fast/multicol/t...
LayoutTests/fast/multicol/transform-with-fixedpos-crash.html:9: <div
style="position:fixed;"></div>
Ideally we would want to test that we get the *correct* result as assertions are
disabled in release and it's also a more meaningful information that not
crashing.

https://codereview.chromium.org/1268493002/diff/1/Source/core/paint/Deprecate...
File Source/core/paint/DeprecatedPaintLayer.cpp (right):

https://codereview.chromium.org/1268493002/diff/1/Source/core/paint/Deprecate...
Source/core/paint/DeprecatedPaintLayer.cpp:1260: // of both relative to the
positioned ancestor and subtract.
s/positioned ancestor/container (as fixed position elements don't stop at
positioned ancestors).

[mstensho (USE GERRIT), 2015-07-30 09:32:07]

https://codereview.chromium.org/1268493002/diff/1/LayoutTests/fast/multicol/t...
File LayoutTests/fast/multicol/transform-with-fixedpos-crash.html (right):

https://codereview.chromium.org/1268493002/diff/1/LayoutTests/fast/multicol/t...
LayoutTests/fast/multicol/transform-with-fixedpos-crash.html:6: <p>PASS if no
crash or assertion failure.</p>
On 2015/07/29 23:10:52, Julien Chaffraix - PST wrote:
> Let's add a description of what is tested.

Done.

https://codereview.chromium.org/1268493002/diff/1/LayoutTests/fast/multicol/t...
LayoutTests/fast/multicol/transform-with-fixedpos-crash.html:9: <div
style="position:fixed;"></div>
On 2015/07/29 23:10:52, Julien Chaffraix - PST wrote:
> Ideally we would want to test that we get the *correct* result as assertions
are
> disabled in release and it's also a more meaningful information that not
> crashing.

Done.

Made a reftest instead. Note that there are still a bug with fixed-positioneds
here, not related to this part of the code, so the test is somewhat crippled, in
that it's boring enough to let everything take place in the first column, to
avoid exposing other said bug. See bug 515415.

https://codereview.chromium.org/1268493002/diff/1/Source/core/paint/Deprecate...
File Source/core/paint/DeprecatedPaintLayer.cpp (right):

https://codereview.chromium.org/1268493002/diff/1/Source/core/paint/Deprecate...
Source/core/paint/DeprecatedPaintLayer.cpp:1260: // of both relative to the
positioned ancestor and subtract.
On 2015/07/29 23:10:52, Julien Chaffraix - PST wrote:
> s/positioned ancestor/container (as fixed position elements don't stop at
> positioned ancestors).

Done.

[mstensho (USE GERRIT), 2015-07-30 09:32:34]

The CQ bit was checked by mstensho@opera.com

[mstensho (USE GERRIT), 2015-07-30 09:32:35]

The patchset sent to the CQ was uploaded after l-g-t-m from
jchaffraix@chromium.org
Link to the patchset: https://codereview.chromium.org/1268493002/#ps40001
(title: "Fix comment")

[commit-bot: I haz the power, 2015-07-30 09:32:40]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1268493002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1268493002/40001

[commit-bot: I haz the power, 2015-07-30 10:34:51]

Committed patchset #3 (id:40001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=199725