Introduce base::IsWeakReceiver for base::Bind to support external weak pointers

Introduce base::IsWeakReceiver for base::Bind to support external weak pointers

base::IsWeakReceiver is an injection point for external libraries to
configure a receiver to behave as a weak pointer. Namely, WTF::WeakPtr,
WTF::WeakPersistent and WTF::CrossThreadWeakPersistent in Blink will be
specialize base::IsWeakReceiver, and the callback will be cancelled on
null instances of them.

Committed: https://crrev.com/1ae80b2655df4f23b87776625de2ae8eb0e03df2
Cr-Commit-Position: refs/heads/master@{#399689}

[tzik, 2016-06-10 06:22:36]

Description was changed from

==========
Introduce base::IsWeakReceiver for base::Bind to support external weak pointers

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

to

==========
Introduce base::IsWeakReceiver for base::Bind to support external weak pointers

base::IsWeakReceiver is an injection point for external libraries to
configure a receiver to behave as a weak pointer. Namely, WTF::WeakPtr,
WTF::WeakPersistent and WTF::CrossThreadWeakPersistent in Blink will be
specialize base::IsWeakReceiver, and the callback will be cancelled on
null instances of them.
==========

[tzik, 2016-06-10 06:23:10]

tzik@chromium.org changed reviewers:
+ danakj@chromium.org

[tzik, 2016-06-10 06:23:11]

PTAL

[danakj, 2016-06-10 23:36:18]

Few small comments, LGTM overall

https://codereview.chromium.org/2048023004/diff/20001/base/bind_helpers.h
File base/bind_helpers.h (right):

https://codereview.chromium.org/2048023004/diff/20001/base/bind_helpers.h#new...
base/bind_helpers.h:631: // method, base::Bind cancels the method invocation if
the receiver is null.
"if the receiver is tested as false" may be more accurate. Or something similar.

https://codereview.chromium.org/2048023004/diff/20001/base/bind_helpers.h#new...
base/bind_helpers.h:646: struct IsWeakReceiver<internal::ConstRefWrapper<T>> :
IsWeakReceiver<T> {};
nit: Does it compile if you put this above the WeakPtr one? I'm guess you intend
to add other things to the list, so grouping them at the bottom of the set of
defns might be nice.

https://codereview.chromium.org/2048023004/diff/20001/base/bind_internal.h
File base/bind_internal.h (right):

https://codereview.chromium.org/2048023004/diff/20001/base/bind_internal.h#ne...
base/bind_internal.h:326: weak_ptr, std::forward<RunArgs>(args)...);
I had to look at a bunch of places to understand why weak_ptr didn't need to be
moved here. Run takes a Receiver&&, but BoundWeakPtr will actually be a const&
since that is what Unwrap returns, IIUC.

It might be more obvious/less hidden, if you make |weak_ptr| be a forwarding
reference like the other arguments to this method with a &&, and forward it
here?

[tzik, 2016-06-14 12:06:10]

https://codereview.chromium.org/2048023004/diff/20001/base/bind_helpers.h
File base/bind_helpers.h (right):

https://codereview.chromium.org/2048023004/diff/20001/base/bind_helpers.h#new...
base/bind_helpers.h:631: // method, base::Bind cancels the method invocation if
the receiver is null.
On 2016/06/10 23:36:18, danakj wrote:
> "if the receiver is tested as false" may be more accurate. Or something
similar.

Done.

https://codereview.chromium.org/2048023004/diff/20001/base/bind_helpers.h#new...
base/bind_helpers.h:646: struct IsWeakReceiver<internal::ConstRefWrapper<T>> :
IsWeakReceiver<T> {};
On 2016/06/10 23:36:17, danakj wrote:
> nit: Does it compile if you put this above the WeakPtr one? I'm guess you
intend
> to add other things to the list, so grouping them at the bottom of the set of
> defns might be nice.

Done.

https://codereview.chromium.org/2048023004/diff/20001/base/bind_internal.h
File base/bind_internal.h (right):

https://codereview.chromium.org/2048023004/diff/20001/base/bind_internal.h#ne...
base/bind_internal.h:326: weak_ptr, std::forward<RunArgs>(args)...);
On 2016/06/10 23:36:18, danakj wrote:
> I had to look at a bunch of places to understand why weak_ptr didn't need to
be
> moved here. Run takes a Receiver&&, but BoundWeakPtr will actually be a const&
> since that is what Unwrap returns, IIUC.
> 
> It might be more obvious/less hidden, if you make |weak_ptr| be a forwarding
> reference like the other arguments to this method with a &&, and forward it
> here?

Done.

[tzik, 2016-06-14 12:38:23]

The CQ bit was checked by tzik@chromium.org

[tzik, 2016-06-14 12:38:24]

The patchset sent to the CQ was uploaded after l-g-t-m from danakj@chromium.org
Link to the patchset: https://codereview.chromium.org/2048023004/#ps40001
(title: "comment fix. reorder template specializations. use Perfect Forwarding
for weak call")

[commit-bot: I haz the power, 2016-06-14 12:38:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2048023004/40001

[commit-bot: I haz the power, 2016-06-14 13:17:47]

Description was changed from

==========
Introduce base::IsWeakReceiver for base::Bind to support external weak pointers

base::IsWeakReceiver is an injection point for external libraries to
configure a receiver to behave as a weak pointer. Namely, WTF::WeakPtr,
WTF::WeakPersistent and WTF::CrossThreadWeakPersistent in Blink will be
specialize base::IsWeakReceiver, and the callback will be cancelled on
null instances of them.
==========

to

==========
Introduce base::IsWeakReceiver for base::Bind to support external weak pointers

base::IsWeakReceiver is an injection point for external libraries to
configure a receiver to behave as a weak pointer. Namely, WTF::WeakPtr,
WTF::WeakPersistent and WTF::CrossThreadWeakPersistent in Blink will be
specialize base::IsWeakReceiver, and the callback will be cancelled on
null instances of them.
==========

[commit-bot: I haz the power, 2016-06-14 13:17:48]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2016-06-14 13:17:57]

CQ bit was unchecked

[commit-bot: I haz the power, 2016-06-14 13:21:18]

Description was changed from

==========
Introduce base::IsWeakReceiver for base::Bind to support external weak pointers

base::IsWeakReceiver is an injection point for external libraries to
configure a receiver to behave as a weak pointer. Namely, WTF::WeakPtr,
WTF::WeakPersistent and WTF::CrossThreadWeakPersistent in Blink will be
specialize base::IsWeakReceiver, and the callback will be cancelled on
null instances of them.
==========

to

==========
Introduce base::IsWeakReceiver for base::Bind to support external weak pointers

base::IsWeakReceiver is an injection point for external libraries to
configure a receiver to behave as a weak pointer. Namely, WTF::WeakPtr,
WTF::WeakPersistent and WTF::CrossThreadWeakPersistent in Blink will be
specialize base::IsWeakReceiver, and the callback will be cancelled on
null instances of them.

Committed: https://crrev.com/1ae80b2655df4f23b87776625de2ae8eb0e03df2
Cr-Commit-Position: refs/heads/master@{#399689}
==========

[commit-bot: I haz the power, 2016-06-14 13:21:19]

Patchset 3 (id:??) landed as
https://crrev.com/1ae80b2655df4f23b87776625de2ae8eb0e03df2
Cr-Commit-Position: refs/heads/master@{#399689}