[New Multicolumn] Don't enter child multicol contexts when processing object insertions / removals.

[New Multicolumn] Don't enter child multicol contexts when processing object insertions / removals.

If we were to process a descendant flow thread and its descendants, we would
need to descend into it properly, by calling flowThreadDescendantWasInserted()
/ flowThreadDescendantWillBeRemoved() on the inner flow thread for all its
children (instead of erroneously pretending that the inner flow thread's
children were part of the outer flow thread). But instead of doing all that,
just skip the whole thing. When whole subtrees are inserted or removed, it's
typically done via moveChildTo() & co, and we can safely leave inner flow
threads (and their associated column sets and spanner placeholders) as they
are. The move will not affect them. They will be exactly as much multicol
before and after the move.

Also rename a local variable from |nextRenderer| to |objectAfterSubtree| to
avoid confusion with the new variable |next|.

Similarly, only update the flow thread state flag for the objects that actually
belong to a given flow thread (i.e. don't descend into descendant flow
threads).

BUG=479126
R=dsinclair@chromium.org,jchaffraix@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=194402

[dsinclair, 2015-04-24 13:13:30]

lgtm w/ nit.

https://codereview.chromium.org/1109513002/diff/1/Source/core/layout/LayoutMu...
File Source/core/layout/LayoutMultiColumnFlowThread.cpp (right):

https://codereview.chromium.org/1109513002/diff/1/Source/core/layout/LayoutMu...
Source/core/layout/LayoutMultiColumnFlowThread.cpp:474: for (LayoutObject*
renderer = descendant; renderer; renderer = next) {
nit: s/renderer/layoutObject/

[mstensho (USE GERRIT), 2015-04-24 13:27:26]

https://codereview.chromium.org/1109513002/diff/1/Source/core/layout/LayoutMu...
File Source/core/layout/LayoutMultiColumnFlowThread.cpp (right):

https://codereview.chromium.org/1109513002/diff/1/Source/core/layout/LayoutMu...
Source/core/layout/LayoutMultiColumnFlowThread.cpp:474: for (LayoutObject*
renderer = descendant; renderer; renderer = next) {
On 2015/04/24 13:13:30, dsinclair wrote:
> nit: s/renderer/layoutObject/

Done.

Note that I didn't really introduce this in this CL, though.

[mstensho (USE GERRIT), 2015-04-24 13:27:43]

The CQ bit was checked by mstensho@opera.com

[mstensho (USE GERRIT), 2015-04-24 13:27:44]

The patchset sent to the CQ was uploaded after l-g-t-m from
dsinclair@chromium.org
Link to the patchset: https://codereview.chromium.org/1109513002/#ps20001
(title: "code review: renderer -> layoutObject")

[commit-bot: I haz the power, 2015-04-24 13:27:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1109513002/20001

[commit-bot: I haz the power, 2015-04-24 16:10:10]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=194402