The crash happens if the thread is created but never started. An
improper Join triggered the crash. We should not call Join if the thread
is not started.
Change-Id: Icace740889089d3b2e15cf6c76c2b0887eb84535
ClosureThread runs a Closure in a platform thread. Chromium Thread class
involves message loop, so we choose to implement our own based on the
lower level SimpleThread which wraps PlatformThread.
Change-Id: Ibb759f7debcc027c0764195ca93506f9a202110b