Revert 110361 - NaCl: preallocate shared-memory object on Linux as on MacOSX

chrome/browser/nacl_host/nacl_process_host.cc

Index: chrome/browser/nacl_host/nacl_process_host.cc
===================================================================
--- chrome/browser/nacl_host/nacl_process_host.cc	(revision 110775)
+++ chrome/browser/nacl_host/nacl_process_host.cc	(working copy)
@@ -486,11 +486,11 @@
     return;
   }
 
-#if defined(OS_POSIX)
-  // For dynamic loading support, NaCl requires a file descriptor on an
-  // anonymous file that can have PROT_EXEC applied to its mappings.
-  // Rather than requiring an extra IPC round trip out of the sandbox,
-  // we create an FD here.
+#if defined(OS_MACOSX)
+  // For dynamic loading support, NaCl requires a file descriptor that
+  // was created in /tmp, since those created with shm_open() are not
+  // mappable with PROT_EXEC.  Rather than requiring an extra IPC
+  // round trip out of the sandbox, we create an FD here.
   base::SharedMemory memory_buffer;
   if (!memory_buffer.CreateAnonymous(/* size= */ 1)) {
     LOG(ERROR) << "Failed to allocate memory buffer";