[Line Layout API] Add nullptr constructors to all LineLayoutItem descendants

[Line Layout API] Add nullptr constructors to all LineLayoutItem descendants

This came up in another CL ( https://codereview.chromium.org/1433253003/ )
where we needed to nullify a private LineLayoutText object and couldn't do
the obvious m_lineLayoutText=nullptr solution. This CL will let anyone do
the obvious thing and have it work properly, without casting or separate
methods.

BUG=499321
Committed: https://crrev.com/f85fc03a7ec41b34073d25044dc3495b266724a0
Cr-Commit-Position: refs/heads/master@{#360971}

[pilgrim_google, 2015-11-19 21:49:17]

pilgrim@chromium.org changed reviewers:
+ eae@chromium.org, jsbell@chromium.org, leviw@chromium.org

[jsbell, 2015-11-19 22:06:40]

https://codereview.chromium.org/1460923003/diff/1/third_party/WebKit/Source/c...
File third_party/WebKit/Source/core/layout/api/LineLayoutBlockFlow.h (right):

https://codereview.chromium.org/1460923003/diff/1/third_party/WebKit/Source/c...
third_party/WebKit/Source/core/layout/api/LineLayoutBlockFlow.h:33:
LineLayoutBlockFlow(std::nullptr_t) : LineLayoutBox(nullptr) { }
Drive-by: can we add `explicit` qualifier here (and other single-argument
ctors)?

This will prevent unexpected coercion. It would also prevent `foo = 0` but we
should patch those up to be `foo = nullptr` anyway.

OWNERS may disagree if we have too many cases of `... = 0` in the code, though.

[pilgrim_google, 2015-11-20 14:46:09]

On 2015/11/19 at 22:06:40, jsbell wrote:
>
https://codereview.chromium.org/1460923003/diff/1/third_party/WebKit/Source/c...
> File third_party/WebKit/Source/core/layout/api/LineLayoutBlockFlow.h (right):
> 
>
https://codereview.chromium.org/1460923003/diff/1/third_party/WebKit/Source/c...
> third_party/WebKit/Source/core/layout/api/LineLayoutBlockFlow.h:33:
LineLayoutBlockFlow(std::nullptr_t) : LineLayoutBox(nullptr) { }
> Drive-by: can we add `explicit` qualifier here (and other single-argument
ctors)?
> 
> This will prevent unexpected coercion. It would also prevent `foo = 0` but we
should patch those up to be `foo = nullptr` anyway.
> 
> OWNERS may disagree if we have too many cases of `... = 0` in the code,
though.

This went well.

[leviw_travelin_and_unemployed, 2015-11-20 21:05:34]

lgtm

[pilgrim_google, 2015-11-20 23:27:25]

The CQ bit was checked by pilgrim@chromium.org

[commit-bot: I haz the power, 2015-11-20 23:28:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1460923003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1460923003/20001

[commit-bot: I haz the power, 2015-11-21 01:05:11]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-21 01:06:18]

Patchset 2 (id:??) landed as
https://crrev.com/f85fc03a7ec41b34073d25044dc3495b266724a0
Cr-Commit-Position: refs/heads/master@{#360971}