Switch ThreadCheckerImpl over to using PlatformThreadRef.
Like PlatformThreadId, this type is borrowed from Chromium.
The difference between the two is that PlatformThreadRef is pthread_t on posix platforms.
On Windows PlatformThreadRef and PlatformThreadId are the same thing.

The reason for this switch is pretty crazy.  On Chromium's "Mac 10.9 dbg" bot,
we have been seeing the following code:

ThreadCheckerImpl::ThreadCheckerImpl() : valid_thread_(CurrentThreadId()) {
  fprintf(stderr, "*** valid=%d\n", valid_thread_);
  valid_thread_ = CurrentThreadId();
  fprintf(stderr, "*** valid after=%d\n", valid_thread_);
}

print this:

*** valid=946872320
*** valid after=5647

This is for the same thread checker instance.

What's worse is that printing out what CurrentThreadId was returning, yielded that it was always returning 5647.

After switching over to pthread_t on Mac, this stopped happening.
So, to remove the current hack, reinstate the class on Mac and take a look at the next problem, I'm switching to pthread_t.
Really looking forward to truly getting to the bottom of this.

Tbr-ing since the build is essentially broken (we can't roll).

TBR=pbos@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/37199004

Cr-Commit-Position: refs/heads/master@{#8283}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8283 4adac7df-926f-26a2-2b94-8c16560cd09d
3 files changed