Add CallOnce() and simple LazyInstance implementation.

Add CallOnce() and simple LazyInstance implementation.

Note that this implementation of LazyInstance does not handle global destructors (i.e. the lazy instances are never deleted).

This CL was initially reviewed on codereview.appspot.com:
http://codereview.appspot.com/5687064/

BUG=1859

[fschneider, 2012-02-24 12:01:00]

Still LGTM.

[Dmitry Vyukov, 2012-02-24 12:09:32]

LGTM

[jbates, 2012-02-24 17:31:56]

lgtm

[Philippe, 2012-02-27 10:15:36]

On 2012/02/24 17:31:56, jbates wrote:
> lgtm

I uploaded a new patch set. The previous if statements in CallOnce(), in once.h
were out-dated.
The atomic word visible in the header was initially used as a boolean.
Now it has three states, therefore the condition could be satisfied while the
initialization function was still running (state = 1) which was obviously a bug.

[Philippe, 2012-02-27 14:07:38]

On 2012/02/27 10:15:36, Philippe wrote:
> On 2012/02/24 17:31:56, jbates wrote:
> > lgtm
> 
> I uploaded a new patch set. The previous if statements in CallOnce(), in
once.h
> were out-dated.
> The atomic word visible in the header was initially used as a boolean.
> Now it has three states, therefore the condition could be satisfied while the
> initialization function was still running (state = 1) which was obviously a
bug.

I had to introduce some typedefs to make presubmit.py pass. Cpplint does not
like function pointer syntax in function arguments.