Replace OS_LINUX ifdefs with OS_POSIX & !OS_MACOSX, TOOLKIT_USES_GTK, or

content/gpu/gpu_child_thread.cc

Index: content/gpu/gpu_child_thread.cc
diff --git a/content/gpu/gpu_child_thread.cc b/content/gpu/gpu_child_thread.cc
index d3e6e949b60707fedc11760844073f4df73412da..b84ac0f2a3284e44dde43d0836bdbdd7246c92b4 100644
--- a/content/gpu/gpu_child_thread.cc
+++ b/content/gpu/gpu_child_thread.cc
@@ -89,7 +89,7 @@ bool GpuChildThread::Send(IPC::Message* msg) {
   // process. This could result in deadlock. Unfortunately linux does this for
   // GpuHostMsg_ResizeXID. TODO(apatrick): fix this before issuing any GL calls
   // on the browser process' GPU thread.
-#if !defined(OS_LINUX)
+#if !defined(TOOLKIT_USES_GTK)
     DCHECK(!msg->is_sync());
 #endif