Add experiments link to the options page

This link points to the experiments page, and is only shown in
non-release versions of the extension.

Change-Id: I09db9e6ded29be7f6f03f97378cd9311f88d40d3
diff --git a/src/common/common.js b/src/common/common.js
index db20409..619d6d8 100644
--- a/src/common/common.js
+++ b/src/common/common.js
@@ -150,3 +150,9 @@
   return manifest.browser_specific_settings !== undefined &&
       manifest.browser_specific_settings.gecko !== undefined;
 }
+
+// Returns whether the extension is a release version.
+function isReleaseVersion() {
+  var manifest = chrome.runtime.getManifest();
+  return ('version' in manifest) && manifest.version != '0';
+}