Add a component installer for Portable NaCl. Registration of installer is

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 3dd62e41fe7b3d7c90a9fc18b28b5e240a6aa514..b9f5be7c5d034d56570515d56d0081106559573e 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -517,6 +517,9 @@ const char kEnablePlatformApps[]            = "enable-platform-apps";
 const char kEnableResourceContentSettings[] =
     "enable-resource-content-settings";
 
+// Enables the installation and usage of Portable Native Client.
+const char kEnablePnacl[]                    = "enable-pnacl";
+
 // Enables speculative TCP/IP preconnection.
 const char kEnablePreconnect[]              = "enable-preconnect";