Fix base::Optional constexpr ctor on gcc 4.8.

Fix base::Optional constexpr ctor on gcc 4.8.

g++ 4.8 failed to compile base::Optional<std::unique_ptr<int>>().
A simpler example is:

class C {
 public:
  constexpr C() {}
  ~C() {}

 private:
  union {
    char empty_ = '\0';
    std::unique_ptr<int> value_;
  };
};

g++ 4.8 fails to compile this. But adding empty_('\0') to member
initializer list makes it happy.

This patch does the same for both OptionalStorage default constructors.

BUG=

Committed: https://crrev.com/a637f25fb515f8e860bc941cc1cb24b7862f3c5b
Cr-Commit-Position: refs/heads/master@{#427850}

[alshabalin, 2016-10-26 11:46:33]

alshabalin@yandex-team.ru changed reviewers:
+ danakj@chromium.org

[alshabalin, 2016-10-26 11:46:34]

This is a follow up CL to https://codereview.chromium.org/2434253003/ fixing
compilation with g++ 4.8.

[Mostyn Bramley-Moore, 2016-10-26 12:23:46]

Works for me.

[danakj, 2016-10-26 18:56:49]

https://codereview.chromium.org/2453733002/diff/1/base/optional.h
File base/optional.h (right):

https://codereview.chromium.org/2453733002/diff/1/base/optional.h#newcode64
base/optional.h:64: char empty_ = '\0';
can you drop the \0 here then cuz it's redundant

https://codereview.chromium.org/2453733002/diff/1/base/optional.h#newcode96
base/optional.h:96: char empty_ = '\0';
same

[danakj, 2016-10-26 18:56:54]

LGTM

[alshabalin, 2016-10-26 20:42:38]

Also tweaked comments a bit.

https://codereview.chromium.org/2453733002/diff/1/base/optional.h
File base/optional.h (right):

https://codereview.chromium.org/2453733002/diff/1/base/optional.h#newcode64
base/optional.h:64: char empty_ = '\0';
On 2016/10/26 18:56:49, danakj wrote:
> can you drop the \0 here then cuz it's redundant

Done.

https://codereview.chromium.org/2453733002/diff/1/base/optional.h#newcode96
base/optional.h:96: char empty_ = '\0';
On 2016/10/26 18:56:49, danakj wrote:
> same

Done.

[alshabalin, 2016-10-26 20:42:45]

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

[alshabalin, 2016-10-26 20:42:45]

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/2453733002/#ps20001
(title: "Address review comments")

[commit-bot: I haz the power, 2016-10-26 20:43:40]

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, 2016-10-26 22:29:55]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-10-26 22:33:36]

Description was changed from

==========
Fix base::Optional constexpr ctor on gcc 4.8.

g++ 4.8 failed to compile base::Optional<std::unique_ptr<int>>().
A simpler example is:

class C {
 public:
  constexpr C() {}
  ~C() {}

 private:
  union {
    char empty_ = '\0';
    std::unique_ptr<int> value_;
  };
};

g++ 4.8 fails to compile this. But adding empty_('\0') to member
initializer list makes it happy.

This patch does the same for both OptionalStorage default constructors.

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

to

==========
Fix base::Optional constexpr ctor on gcc 4.8.

g++ 4.8 failed to compile base::Optional<std::unique_ptr<int>>().
A simpler example is:

class C {
 public:
  constexpr C() {}
  ~C() {}

 private:
  union {
    char empty_ = '\0';
    std::unique_ptr<int> value_;
  };
};

g++ 4.8 fails to compile this. But adding empty_('\0') to member
initializer list makes it happy.

This patch does the same for both OptionalStorage default constructors.

BUG=

Committed: https://crrev.com/a637f25fb515f8e860bc941cc1cb24b7862f3c5b
Cr-Commit-Position: refs/heads/master@{#427850}
==========

[commit-bot: I haz the power, 2016-10-26 22:33:36]

Patchset 2 (id:??) landed as
https://crrev.com/a637f25fb515f8e860bc941cc1cb24b7862f3c5b
Cr-Commit-Position: refs/heads/master@{#427850}