Port the Thread class properly to Mac and Linux.  This involved porting
PlatformThread and creating an API on PlatformThread to create a native thread
and later join with it.  I also made a few other tweaks to PlatformThread, such
as eliminating the Current() method which appears to be unused.  The
operator==() is also unused, so I killed it as well.

I made a few other miscellaneous cleanups and adjustments.


git-svn-id: svn://svn.chromium.org/chrome/trunk/src@1146 0039d316-1c4b-4281-b951-d872f2087c98
18 files changed