Bug 1339064 - Add layout panel option to nightly options;r=gl

MozReview-Commit-ID: LOMotSUNj9B

--HG--
extra : rebase_source : 912644a94bcc94ed0e40e76e23f732be1bc99232
extra : source : 6433ff5fdc59628f54e29e8fe7ea50fe95cb6b95

devtools/client/framework/toolbox-options.js

@@ -326,6 +326,11 @@ OptionsPanel.prototype = {
       label: "Enable new debugger frontend",
       id: "devtools-new-debugger",
       parentId: "debugger-options"
+    }, {
+      pref: "devtools.layoutview.enabled",
+      label: "Enable layout panel",
+      id: "devtools-layout-panel",
+      parentId: "inspector-options"
     }];
 
     let createPreferenceOption = ({pref, label, id}) => {