Split the PNaCl IRT shim into 3 pieces, and include one piece into IRT.

components/nacl/loader/nacl_listener.cc

Index: components/nacl/loader/nacl_listener.cc
diff --git a/components/nacl/loader/nacl_listener.cc b/components/nacl/loader/nacl_listener.cc
index c35d946d5bbb369ac221ee5e96a359dfb93e94ff..97ddd5df89a7a42f7ef9946764eee7363912f11a 100644
--- a/components/nacl/loader/nacl_listener.cc
+++ b/components/nacl/loader/nacl_listener.cc
@@ -352,6 +352,11 @@ void NaClListener::OnStart(const nacl::NaClStartParams& params) {
     // PNaCl because it might break existing NaCl apps, and this limit
     // is only useful if the dyncode syscalls are disabled.
     args->initial_nexe_max_code_bytes = 32 << 20;  // 32 MB
+
+    // Only enable the IRT shim ppapi hook for PNaCl pexes (not nexes).
+    // TODO(jvoung): Plumb through something indicating that this is PNaCl
+    // instead of relying on enable_dyncode_syscalls.
+    args->enable_irt_shim = 1;
   }
 #if defined(OS_LINUX) || defined(OS_MACOSX)
   args->debug_stub_server_bound_socket_fd = nacl::ToNativeHandle(