Added initial Chrome/Firefox shells

shells/browser/shared/src/contentScript.js

@@ -0,0 +1,52 @@
+/* global chrome */
+
+// proxy from main page to devtools (via the background page)
+var port = chrome.runtime.connect({
+  name: 'content-script',
+});
+
+port.onMessage.addListener(handleMessageFromDevtools);
+port.onDisconnect.addListener(handleDisconnect);
+window.addEventListener('message', handleMessageFromPage);
+
+window.postMessage(
+  {
+    source: 'react-devtools-content-script',
+    hello: true,
+  },
+  '*'
+);
+
+function handleMessageFromDevtools(message) {
+  window.postMessage(
+    {
+      source: 'react-devtools-content-script',
+      payload: message,
+    },
+    '*'
+  );
+}
+
+function handleMessageFromPage(evt) {
+  if (
+    evt.source === window &&
+    evt.data &&
+    evt.data.source === 'react-devtools-bridge'
+  ) {
+    port.postMessage(evt.data.payload);
+  }
+}
+
+function handleDisconnect() {
+  window.removeEventListener('message', handleMessageFromPage);
+  window.postMessage(
+    {
+      source: 'react-devtools-content-script',
+      payload: {
+        type: 'event',
+        evt: 'shutdown',
+      },
+    },
+    '*'
+  );
+}