Use a valid /prefetch argument when launching a process.

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index 1b9d66441fecd52105aaee0b2886e46931f272b8..764ccda015c048a343e9acd5e8ffc48b91dbbf44 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1254,6 +1254,12 @@ const char kForceImmersive[]                = "force-immersive";
 // This flag is only relevant for Windows currently.
 const char kNoNetworkProfileWarning[]       = "no-network-profile-warning";
 
+// /prefetch:# arguments for the browser process launched in background mode and
+// for the watcher process. These constants must be different from the
+// kPrefetchArgument* constants defined in content_switches.cc.
+const char kPrefetchArgumentBrowserBackground[] = "/prefetch:5";
+const char kPrefetchArgumentWatcher[] = "/prefetch:6";
+
 // For the DelegateExecute verb handler to launch Chrome in desktop mode on
 // Windows 8 and higher.  Used when relaunching metro Chrome.
 const char kForceDesktop[]                  = "force-desktop";