Fix UB with LayerTreeImpl::PassSwapPromises usage

Fix UB with LayerTreeImpl::PassSwapPromises usage

C++ reference says: "Unless otherwise specified, all standard library objects
that have been moved from are placed in a valid but unspecified state"
(http://en.cppreference.com/w/cpp/utility/move).
According to this, current CL fixes UB related to
|LayerTreeHost::swap_promise_list_| and |LayerTreeImpl::swap_promise_list_|
incorrect usage.

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Committed: https://crrev.com/fea15b7520e0ef137d5794e03ad30bc033228b7d
Cr-Commit-Position: refs/heads/master@{#412495}

[svartmetal, 2016-08-15 12:02:32]

Description was changed from

==========
Fix UB with LayerTreeImpl::PassSwapPromises usage

C++ reference says: "Unless otherwise specified, all standard library objects
that have been moved from are placed in a valid but unspecified state"
(http://en.cppreference.com/w/cpp/utility/move).
According to this, current CL fixes UB related to
|LayerTreeHost::swap_promise_list_| and |LayerTreeImpl::swap_promise_list_|
incorrect usage.

BUG=
==========

to

==========
Fix UB with LayerTreeImpl::PassSwapPromises usage

C++ reference says: "Unless otherwise specified, all standard library objects
that have been moved from are placed in a valid but unspecified state"
(http://en.cppreference.com/w/cpp/utility/move).
According to this, current CL fixes UB related to
|LayerTreeHost::swap_promise_list_| and |LayerTreeImpl::swap_promise_list_|
incorrect usage.

BUG=
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel
==========

[svartmetal, 2016-08-15 12:04:28]

svartmetal@yandex-team.ru changed reviewers:
+ brianderson@chromium.org, enne@chromium.org

[enne (OOO), 2016-08-15 17:02:06]

Description was changed from

==========
Fix UB with LayerTreeImpl::PassSwapPromises usage

C++ reference says: "Unless otherwise specified, all standard library objects
that have been moved from are placed in a valid but unspecified state"
(http://en.cppreference.com/w/cpp/utility/move).
According to this, current CL fixes UB related to
|LayerTreeHost::swap_promise_list_| and |LayerTreeImpl::swap_promise_list_|
incorrect usage.

BUG=
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel
==========

to

==========
Fix UB with LayerTreeImpl::PassSwapPromises usage

C++ reference says: "Unless otherwise specified, all standard library objects
that have been moved from are placed in a valid but unspecified state"
(http://en.cppreference.com/w/cpp/utility/move).
According to this, current CL fixes UB related to
|LayerTreeHost::swap_promise_list_| and |LayerTreeImpl::swap_promise_list_|
incorrect usage.

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel
==========

[enne (OOO), 2016-08-15 17:02:17]

The CQ bit was checked by enne@chromium.org

[enne (OOO), 2016-08-15 17:02:17]

lgtm

[commit-bot: I haz the power, 2016-08-15 17:02:32]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[brianderson, 2016-08-15 17:05:55]

https://codereview.chromium.org/2245053002/diff/1/cc/trees/layer_tree_host.cc
File cc/trees/layer_tree_host.cc (left):

https://codereview.chromium.org/2245053002/diff/1/cc/trees/layer_tree_host.cc...
cc/trees/layer_tree_host.cc:514:
sync_tree->PassSwapPromises(std::move(swap_promise_list_));
Thanks for catching this!

It would be more straightforward to call swap_promise_list_.clear() after this
line which, looking online, seems to be just as valid.

[enne (OOO), 2016-08-15 17:09:17]

The CQ bit was unchecked by enne@chromium.org

[svartmetal, 2016-08-15 19:04:33]

https://codereview.chromium.org/2245053002/diff/1/cc/trees/layer_tree_host.cc
File cc/trees/layer_tree_host.cc (left):

https://codereview.chromium.org/2245053002/diff/1/cc/trees/layer_tree_host.cc...
cc/trees/layer_tree_host.cc:514:
sync_tree->PassSwapPromises(std::move(swap_promise_list_));
On 2016/08/15 17:05:55, brianderson wrote:
> Thanks for catching this!
> 
> It would be more straightforward to call swap_promise_list_.clear() after this
> line which, looking online, seems to be just as valid.
Fixed. It's OK to use std::vector::clear since it has no preconditions. On the
other hand, it leaves the capacity() of the vector unchanged (maybe it is better
to use assignment operator instead).

[svartmetal, 2016-08-16 09:38:42]

brianderson@, please take another look.

[svartmetal, 2016-08-16 19:33:22]

brianderson@, please take another look.

[brianderson, 2016-08-16 21:42:43]

lgtm

[svartmetal, 2016-08-17 09:54:06]

The CQ bit was checked by svartmetal@yandex-team.ru

[svartmetal, 2016-08-17 09:54:06]

The patchset sent to the CQ was uploaded after l-g-t-m from enne@chromium.org
Link to the patchset: https://codereview.chromium.org/2245053002/#ps20001
(title: "Use std::vector::clear instead")

[commit-bot: I haz the power, 2016-08-17 09:54:20]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-17 11:10:27]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-08-17 11:11:37]

Description was changed from

==========
Fix UB with LayerTreeImpl::PassSwapPromises usage

C++ reference says: "Unless otherwise specified, all standard library objects
that have been moved from are placed in a valid but unspecified state"
(http://en.cppreference.com/w/cpp/utility/move).
According to this, current CL fixes UB related to
|LayerTreeHost::swap_promise_list_| and |LayerTreeImpl::swap_promise_list_|
incorrect usage.

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel
==========

to

==========
Fix UB with LayerTreeImpl::PassSwapPromises usage

C++ reference says: "Unless otherwise specified, all standard library objects
that have been moved from are placed in a valid but unspecified state"
(http://en.cppreference.com/w/cpp/utility/move).
According to this, current CL fixes UB related to
|LayerTreeHost::swap_promise_list_| and |LayerTreeImpl::swap_promise_list_|
incorrect usage.

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Committed: https://crrev.com/fea15b7520e0ef137d5794e03ad30bc033228b7d
Cr-Commit-Position: refs/heads/master@{#412495}
==========

[commit-bot: I haz the power, 2016-08-17 11:11:38]

Patchset 2 (id:??) landed as
https://crrev.com/fea15b7520e0ef137d5794e03ad30bc033228b7d
Cr-Commit-Position: refs/heads/master@{#412495}