Allow constructing {Interface,Struct}Ptr from nullptr

Allow constructing {Interface,Struct}Ptr from nullptr

This allows spelling a null InterfacePtr or StructPtr parameter
'nullptr' instead of namespace::FooPtr(). To do so, this uses C++11
rvalue reference semantics for move support and adds constructor and
assignment operator overloads that take the type decltype(nullptr). We
still use a macro for move-only types to hide the copy and assignment
operators, add Pass(), and add the misleading named type tag
MoveOnlyForCPP03 for compatibility with Chromium's base/callback (and
anything else that may want to use it).

R=darin@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/e4389610d2f6e842ef79786c3100da363fd1b0a3

[jamesr, 2015-01-13 23:27:05]

https://codereview.chromium.org/828373008/diff/1/mojo/public/cpp/bindings/tes...
File mojo/public/cpp/bindings/tests/interface_ptr_unittest.cc (right):

https://codereview.chromium.org/828373008/diff/1/mojo/public/cpp/bindings/tes...
mojo/public/cpp/bindings/tests/interface_ptr_unittest.cc:330:
proxy->Frobinate(nullptr, sample::Service::BAZ_OPTIONS_REGULAR, nullptr);
this is the example use. The first parameter to this function is a StructPtr,
the third is an InterfacePtr.

[jamesr, 2015-01-13 23:27:31]

We could also add overloads for constructing scoped handle types from 'nullptr'
but that's semantically a bit more dubious than the Ptr types.

[jamesr, 2015-01-14 18:33:56]

jamesr@chromium.org changed reviewers:
+ viettrungluu@chromium.org

[jamesr, 2015-01-14 18:33:57]

R += trung

[darin (slow to review), 2015-01-14 18:38:07]

Wow, that's really nice!

https://codereview.chromium.org/828373008/diff/1/mojo/public/cpp/bindings/str...
File mojo/public/cpp/bindings/struct_ptr.h (right):

https://codereview.chromium.org/828373008/diff/1/mojo/public/cpp/bindings/str...
mojo/public/cpp/bindings/struct_ptr.h:117: 
don't you need the nullptr ctor and assignment operator here too?

[darin (slow to review), 2015-01-14 18:38:12]

LGTM

[jamesr, 2015-01-14 18:39:30]

(I stole most of this from Dana's work in base/, fyi)

https://codereview.chromium.org/828373008/diff/1/mojo/public/cpp/bindings/str...
File mojo/public/cpp/bindings/struct_ptr.h (right):

https://codereview.chromium.org/828373008/diff/1/mojo/public/cpp/bindings/str...
mojo/public/cpp/bindings/struct_ptr.h:117: 
On 2015/01/14 18:38:07, darin wrote:
> don't you need the nullptr ctor and assignment operator here too?

Hmm yes - I didn't find a user of this but it'd be nice to use here as well. 
Will add and find somewhere to use it.

[jamesr, 2015-01-14 19:15:19]

Committed patchset #1 (id:1) manually as
e4389610d2f6e842ef79786c3100da363fd1b0a3 (presubmit successful).