Use a valid /prefetch argument when launching a process.

components/nacl/browser/nacl_process_host.cc

Index: components/nacl/browser/nacl_process_host.cc
diff --git a/components/nacl/browser/nacl_process_host.cc b/components/nacl/browser/nacl_process_host.cc
index 3b57e145015f46abe09ffc6803fde16b7b271721..3c0a24f47609fdda5fe8a8834e9fa5b7c9dce20b 100644
--- a/components/nacl/browser/nacl_process_host.cc
+++ b/components/nacl/browser/nacl_process_host.cc
@@ -77,6 +77,7 @@
 #include "base/win/scoped_handle.h"
 #include "components/nacl/browser/nacl_broker_service_win.h"
 #include "components/nacl/common/nacl_debug_exception_handler_win.h"
+#include "components/startup_metric_utils/common/pre_read_field_trial_utils_win.h"
 #include "content/public/common/sandbox_init.h"
 #endif
 
@@ -641,7 +642,12 @@ bool NaClProcessHost::LaunchSelLdr() {
   if (NaClBrowser::GetDelegate()->DialogsAreSuppressed())
     cmd_line->AppendSwitch(switches::kNoErrorDialogs);
 
-  // On Windows we might need to start the broker process to launch a new loader
+#if defined(OS_WIN)
+  if (startup_metric_utils::GetPreReadOptions().prefetch_argument)
+    cmd_line->AppendArg(switches::kPrefetchArgumentOther);
+#endif  // defined(OS_WIN)
+
+// On Windows we might need to start the broker process to launch a new loader
 #if defined(OS_WIN)
   if (RunningOnWOW64()) {
     if (!NaClBrokerService::GetInstance()->LaunchLoader(