Only setup the integration with Redux devtools if dev sets env var

CONTRIBUTING.md

@@ -48,8 +48,10 @@ devtools extension for debugging Gatsby.
 
 To use this, first install
 [redux-devtools-extension](https://github.com/zalmoxisus/redux-devtools-extension)
-in your browser. Then in your Gatsby repo, run `npm run remotedev`. Then
-in your site directory run `gatsby develop`.
+in your browser. Then in your Gatsby repo, run `npm run remotedev`. Then in
+your site directory run `REDUX_DEVTOOLS=true gatsby develop`. Depending on
+your operating system and shell, you may need to modify how you set the
+`REDUX_DEVTOOLS` environment variable.
 
 At this point, your site will be sending Redux actions and state to the remote server.
 

packages/gatsby/lib/redux/index.js

@@ -17,25 +17,24 @@ try {
   // ignore errors.
 }
 
-const sitePackageJSON = require(`${process.cwd()}/package.json`)
-const composeEnhancers = composeWithDevTools({
-  realtime: true,
-  port: 19999,
-  name: sitePackageJSON.name,
-})
-
 let store
-// Don't try connecting to devtools server if testing or building.
-if (process.env.NODE_ENV === `test` || process.env.NODE_ENV === `production`) {
+// Only setup the Redux devtools if explicitly enabled.
+if (process.env.REDUX_DEVTOOLS === `true`) {
+  const sitePackageJSON = require(`${process.cwd()}/package.json`)
+  const composeEnhancers = composeWithDevTools({
+    realtime: true,
+    port: 19999,
+    name: sitePackageJSON.name,
+  })
   store = Redux.createStore(
     Redux.combineReducers({ ...reducers }),
-    initialState
+    initialState,
+    composeEnhancers(Redux.applyMiddleware())
   )
 } else {
   store = Redux.createStore(
     Redux.combineReducers({ ...reducers }),
-    initialState,
-    composeEnhancers(Redux.applyMiddleware())
+    initialState
   )
 }