PPAPI/NaCl: Fix IPC proxy build; pthread_t changed

We broke when NaCl DEPS were rolled, giving us this change:
r8650: (mseaborn) libpthread: Make pthread_t a pointer instead of a small integer ID

BUG=116317
TEST=

Review URL: https://chromiumcodereview.appspot.com/10417026

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@138261 0039d316-1c4b-4281-b951-d872f2087c98

base/threading/platform_thread_posix.cc

@@ -160,8 +160,11 @@ PlatformThreadId PlatformThread::CurrentId() {
   return syscall(__NR_gettid);
 #elif defined(OS_ANDROID)
   return gettid();
-#elif defined(OS_NACL) || defined(OS_SOLARIS)
+#elif defined(OS_SOLARIS)
   return pthread_self();
+#elif defined(OS_NACL)
+  // Pointers are 32-bits in NaCl.
+  return reinterpret_cast<int32>(pthread_self());
 #elif defined(OS_POSIX)
   return reinterpret_cast<int64>(pthread_self());
 #endif