Fix accumulating offsets for fixed positioned layers

Fix accumulating offsets for fixed positioned layers 

This makes accumulateOffsetTowardsAncestor handle the case
where a fixed-pos container has a transform-related property
but not a transform.

BUG=426157
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=194764

[ajuma, 2015-04-30 17:37:30]

ajuma@chromium.org changed reviewers:
+ chrishtr@chromium.org, vollick@chromium.org

[chrishtr, 2015-04-30 17:41:06]

chrishtr@chromium.org changed reviewers:
+ trchen@chromium.org

[chrishtr, 2015-04-30 17:46:01]

https://codereview.chromium.org/1111423002/diff/20001/Source/core/paint/Depre...
File Source/core/paint/DeprecatedPaintLayer.cpp (right):

https://codereview.chromium.org/1111423002/diff/20001/Source/core/paint/Depre...
Source/core/paint/DeprecatedPaintLayer.cpp:1408: if (foundAncestor) {
Why would it not find the ancestor? What does this have to do with the change
here?

[ajuma, 2015-04-30 17:57:15]

https://codereview.chromium.org/1111423002/diff/20001/Source/core/paint/Depre...
File Source/core/paint/DeprecatedPaintLayer.cpp (right):

https://codereview.chromium.org/1111423002/diff/20001/Source/core/paint/Depre...
Source/core/paint/DeprecatedPaintLayer.cpp:1408: if (foundAncestor) {
On 2015/04/30 17:46:01, chrishtr wrote:
> Why would it not find the ancestor? What does this have to do with the change
> here?

The code previously assumed that ancestorLayer was either the
fixedPositionContainerLayer or its descendant. We were hitting the assert (and
rendering incorrectly) when that wasn't the case. With the assert fixed, we
still need to compute the offset correctly for this case (where the
ancestorLayer is also an ancestor of the fixedPositionContainerLayer). We can't
call convertToLayerCoords below in that case, since that expects an ancestor of
ancestorLayer. So instead we only compute the offset up to the
fixedPositionContainerLayer, and allow the loop in the caller to then compute
the offset from the fixedPositionContainerLayer to the ancestorLayer.

[chrishtr, 2015-04-30 18:19:50]

The CQ bit was checked by chrishtr@chromium.org

[chrishtr, 2015-04-30 18:19:50]

lgtm

[commit-bot: I haz the power, 2015-04-30 18:20:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1111423002/20001

[commit-bot: I haz the power, 2015-04-30 18:30:37]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=194764