Add support for chrome.extension API in devtools extension.

atom/renderer/lib/chrome-api.coffee

@@ -0,0 +1,10 @@
+url = require 'url'
+
+chrome = window.chrome = window.chrome || {}
+chrome.extension =
+  getURL: (path) ->
+    url.format
+      protocol: location.protocol
+      slashes: true
+      hostname: location.hostname
+      pathname: path

atom/renderer/lib/init.coffee

@@ -46,6 +46,9 @@ else
 if location.protocol is 'chrome-devtools:'
   # Override some inspector APIs.
   require path.join(__dirname, 'inspector')
+else if location.protocol is 'chrome-extension:'
+  # Add implementations of chrome API.
+  require path.join(__dirname, 'chrome-api')
 else
   # Override default web functions.
   require path.join(__dirname, 'override')