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";

[cpu_(ooo_6.6-7.5), 2011/11/23 01:51:33]

I am not opposed to the switches idea, but you have other choices, for example
you can deploy pnacl only to canary.

Or if you are surfacing pnacl in the about:plugins page then there are even
better options. Let me know if you do.

[jvoung - send to chromium..., 2011/12/14 19:34:31]

Yes a command line doesn't seem very friendly, but I'm not sure we are ready to
enable this for all of canary yet. I'm thinking more of an internal dogfood for
now. 
I'm not really familiar with what should and should not go in about:plugins, but
PNaCl doesn't provide an additional mime handler. It's the NaCl plugin that
handles "application/x-nacl", and then may invoke PNaCl. Though it would be nice
to show the version of PNaCl somewhere for debugging.

+
 // Enables speculative TCP/IP preconnection.
 const char kEnablePreconnect[]              = "enable-preconnect";