Add base::LazyInstance

Add base::LazyInstance.

This is changed from the upstream in these ways:
 - mini_chromium’s LazyInstance cannot be used with traits that specify
   kRegisterOnExit. This means that DefaultLazyInstanceTraits are
   unusable, but LeakyLazyInstanceTraits and LazyInstance<>::Leaky are
   usable. kRegisterOnExit is not supported to avoid bringing in
   AtExitManager. The kRegisterOnExit traits constant is still present
   to maintain interface compatibility with mini_chromium, but a
   static_assert ensures that it is always false.
 - BASE_EXPORT is removed as in the rest of mini_chromium.
 - base/debug/leak_annotations.h is removed as it is unnecessary.
 - base/threading/thread_restrictions.h is removed as it is only used to
   implement a debug-mode check that is useless in mini_chromium and
   useless when kRegisterOnExit cannot be true.
 - base/threading/platform_thread.h is removed. A ThreadYield() function
   is provided here.

BUG=crashpad:26
R=rsesek@chromium.org

Committed: https://chromium.googlesource.com/chromium/mini_chromium/+/4870f18a33a6047f2ed0cd7cc78a6f8377f3d7fd

[Mark Mentovai, 2015-03-27 21:34:12]

mark@chromium.org changed reviewers:
+ rsesek@chromium.org

[Robert Sesek, 2015-03-30 15:22:41]

lgtm

[Mark Mentovai, 2015-03-30 15:43:06]

Committed patchset #1 (id:1) manually as
4870f18a33a6047f2ed0cd7cc78a6f8377f3d7fd (presubmit successful).