Added devtools detection.

assets/js/devtools.js

@@ -0,0 +1,9 @@
+// Create a connection to the background page
+var backgroundPageConnection = chrome.runtime.connect({
+    name: "devtools-page"
+});
+
+backgroundPageConnection.postMessage({
+    name: 'init',
+    tabId: chrome.devtools.inspectedWindow.tabId
+});