Use a valid /prefetch argument when launching a process.

chrome/app/chrome_watcher_command_line_win.cc

Index: chrome/app/chrome_watcher_command_line_win.cc
diff --git a/chrome/app/chrome_watcher_command_line_win.cc b/chrome/app/chrome_watcher_command_line_win.cc
index 9c8106b3fdba1cad2624370138d0ade95d39bedc..2f79dbc700dec19f60e8bcfa95682a2224c2c190 100644
--- a/chrome/app/chrome_watcher_command_line_win.cc
+++ b/chrome/app/chrome_watcher_command_line_win.cc
@@ -15,6 +15,7 @@
 #include "base/strings/stringprintf.h"
 #include "base/win/win_util.h"
 #include "chrome/common/chrome_switches.h"
+#include "components/startup_metric_utils/common/pre_read_field_trial_utils_win.h"
 #include "content/public/common/content_switches.h"
 
 namespace {
@@ -154,6 +155,12 @@ base::CommandLine GenerateChromeWatcherCommandLine(
   AppendHandleSwitch(kOnIninitializedEventHandleSwitch, on_initialized_event,
                      &command_line);
   AppendHandleSwitch(kParentHandleSwitch, parent_process, &command_line);
+
+#if defined(OS_WIN)
+  if (startup_metric_utils::GetPreReadOptions().use_prefetch_argument)
+    command_line.AppendArg(switches::kPrefetchArgumentWatcher);
+#endif  // defined(OS_WIN)
+
   return command_line;
 }