adding example of protocol_handlers (mdn#451)

Thanks @tsl143  all looking good.

examples.json

@@ -582,5 +582,10 @@
             "windows​.Window"
         ],
         "name": "window-manipulator"
+    },
+    {
+        "description": "Demonstrates the use of protocol handlers.",
+        "javascript_apis": [],
+        "name": "open-irc-links"
     }
 ]

open-irc-links/README.md

@@ -0,0 +1,14 @@
+# open-irc-links
+
+
+## What it does
+
+This add-on sets the default client for opening IRC links using `protocol_handlers`.
+
+Whenever a link using the IRC protocol is clicked, the link is opened in the URI defined in the add-on's manifest.
+In this example, all IRC protocol links are opened in mibbit.com.  
+For example, once you've installed the extension, click this link [irc://irc.freenode.net/drupal](irc://irc.freenode.net/drupal) and the protocol handler opens the Drupal channel in mibbit.com.
+
+## What it shows
+
+How to use protocol handlers to pass content to an application or website designed to handle that content.

open-irc-links/manifest.json

@@ -0,0 +1,16 @@
+{
+  "manifest_version": 2,
+  "name": "IRC Protocol Handler",
+  "description": "Demos the usage of protocol_handlers",
+  "version": "1.0.0",
+  "icons": {
+    "64": "icons/icon.png"
+  },
+  "protocol_handlers": [
+    {
+      "protocol": "irc",
+      "name": "IRC Mibbit Extension",
+      "uriTemplate": "https://mibbit.com/?url=%s"
+    }
+  ]
+}