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 1a2a2dc50641903ee086af25703db1eecc643e1c..0718b18e8eb16591455355be798c595656b0fcdf 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -536,6 +536,9 @@ 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";