Continue with the FreeBSD port - this version builds and links, though...

base/platform_thread_posix.cc

Index: base/platform_thread_posix.cc
===================================================================
--- base/platform_thread_posix.cc	(revision 25977)
+++ base/platform_thread_posix.cc	(working copy)
@@ -35,6 +35,9 @@
   return mach_thread_self();
 #elif defined(OS_LINUX)
   return syscall(__NR_gettid);
+#elif defined(OS_FREEBSD)
+  // TODO(benl): find a better thread ID
+  return reinterpret_cast<int32>(pthread_self());
 #endif
 }