Enable GTest thread safety on Native Client.

include/gtest/internal/gtest-port.h

@@ -635,13 +635,13 @@ struct _RTL_CRITICAL_SECTION;
 
 // Determines whether Google Test can use the pthreads library.
 #ifndef GTEST_HAS_PTHREAD
-// The user didn't tell us explicitly, so we assume pthreads support is
-// available on Linux and Mac.
+// The user didn't tell us explicitly, so we make reasonable assumptions about
+// which platforms have pthreads support.
 //
 // To disable threading support in Google Test, add -DGTEST_HAS_PTHREAD=0
 // to your compiler flags.
 # define GTEST_HAS_PTHREAD (GTEST_OS_LINUX || GTEST_OS_MAC || GTEST_OS_HPUX \
-    || GTEST_OS_QNX || GTEST_OS_FREEBSD)
+    || GTEST_OS_QNX || GTEST_OS_FREEBSD || GTEST_OS_NACL)
 #endif  // GTEST_HAS_PTHREAD
 
 #if GTEST_HAS_PTHREAD