Add ListContainer::swap

Add ListContainer::swap

This patch implements a simple swap function on ListContainer. This is
the blink-side version of https://codereview.chromium.org/1199343004.
This is one more requirement for backing DisplayItemList by a
ListContainer.

BUG=484943
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=197772

[pdr., 2015-06-24 18:10:36]

pdr@chromium.org changed reviewers:
+ chrishtr@chromium.org, danakj@chromium.org

[chrishtr, 2015-06-24 18:12:28]

https://codereview.chromium.org/1207773003/diff/1/Source/platform/graphics/Li...
File Source/platform/graphics/ListContainerTest.cpp (right):

https://codereview.chromium.org/1207773003/diff/1/Source/platform/graphics/Li...
Source/platform/graphics/ListContainerTest.cpp:953:
EXPECT_EQ(kMagicNumberToUseForSimpleDerivedElementTwo,
list2.front()->getValue());
same comment

[pdr., 2015-06-24 18:18:51]

On 2015/06/24 at 18:12:28, chrishtr wrote:
>
https://codereview.chromium.org/1207773003/diff/1/Source/platform/graphics/Li...
> File Source/platform/graphics/ListContainerTest.cpp (right):
> 
>
https://codereview.chromium.org/1207773003/diff/1/Source/platform/graphics/Li...
> Source/platform/graphics/ListContainerTest.cpp:953:
EXPECT_EQ(kMagicNumberToUseForSimpleDerivedElementTwo,
list2.front()->getValue());
> same comment

I think this was correct but it's a problem if that wasn't obvious. I've
refactored this code to make it a little more clear, and changed the lists so
that we use a magic 2 and a magic 3 instead of two magic 2's.

LGTY?

[chrishtr, 2015-06-24 18:19:27]

The CQ bit was checked by chrishtr@chromium.org

[chrishtr, 2015-06-24 18:19:28]

lgtm

[commit-bot: I haz the power, 2015-06-24 18:20:10]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1207773003/20001

[commit-bot: I haz the power, 2015-06-24 19:23:40]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=197772