Move code for locating the containing flow thread out of LayoutObject.

Move code for locating the containing flow thread out of LayoutObject.

BUG=447718
R=leviw@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=200345

[leviw_travelin_and_unemployed, 2015-08-11 17:51:07]

https://codereview.chromium.org/1286693003/diff/1/Source/core/layout/LayoutFl...
File Source/core/layout/LayoutFlowThread.cpp (right):

https://codereview.chromium.org/1286693003/diff/1/Source/core/layout/LayoutFl...
Source/core/layout/LayoutFlowThread.cpp:49: LayoutObject* curr =
const_cast<LayoutObject*>(&descendant);
What fails in this function if you remove this const_cast?

[mstensho (USE GERRIT), 2015-08-11 19:09:18]

https://codereview.chromium.org/1286693003/diff/1/Source/core/layout/LayoutFl...
File Source/core/layout/LayoutFlowThread.cpp (right):

https://codereview.chromium.org/1286693003/diff/1/Source/core/layout/LayoutFl...
Source/core/layout/LayoutFlowThread.cpp:49: LayoutObject* curr =
const_cast<LayoutObject*>(&descendant);
On 2015/08/11 17:51:07, leviw wrote:
> What fails in this function if you remove this const_cast?

toLayoutFlowThread(), because the constness of input and output have to agree,
so we get the one that takes const returns const, and this methods returns (and
has to return) non-const.

Note that I'm not introducing any const cast with this patch, though. It used to
live in LayoutObject, but now I'm moving it here.

Other methods that do similar things (i.e. find something in the ancestry), such
as LayoutBlock* LayoutObject::containingBlock() const, shake off the constness
debuff by starting at their parent(). In this method we start at ourselves.

[leviw_travelin_and_unemployed, 2015-08-11 19:13:10]

On 2015/08/11 at 19:09:18, mstensho wrote:
>
https://codereview.chromium.org/1286693003/diff/1/Source/core/layout/LayoutFl...
> File Source/core/layout/LayoutFlowThread.cpp (right):
> 
>
https://codereview.chromium.org/1286693003/diff/1/Source/core/layout/LayoutFl...
> Source/core/layout/LayoutFlowThread.cpp:49: LayoutObject* curr =
const_cast<LayoutObject*>(&descendant);
> On 2015/08/11 17:51:07, leviw wrote:
> > What fails in this function if you remove this const_cast?
> 
> toLayoutFlowThread(), because the constness of input and output have to agree,
so we get the one that takes const returns const, and this methods returns (and
has to return) non-const.
Thanks!

> 
> Note that I'm not introducing any const cast with this patch, though. It used
to live in LayoutObject, but now I'm moving it here.
No worries I saw that :)

> 
> Other methods that do similar things (i.e. find something in the ancestry),
such as LayoutBlock* LayoutObject::containingBlock() const, shake off the
constness debuff by starting at their parent(). In this method we start at
ourselves.

LGTM

[leviw_travelin_and_unemployed, 2015-08-11 19:13:15]

The CQ bit was checked by leviw@chromium.org

[commit-bot: I haz the power, 2015-08-11 19:13:23]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1286693003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1286693003/1

[commit-bot: I haz the power, 2015-08-11 19:16:13]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=200345