Implement a simple content script injector

filenames.gypi

@@ -49,6 +49,7 @@
       'lib/common/init.js',
       'lib/common/reset-search-paths.js',
       'lib/renderer/chrome-api.js',
+      'lib/renderer/content-scripts-injector.js',
       'lib/renderer/init.js',
       'lib/renderer/inspector.js',
       'lib/renderer/override.js',

lib/browser/chrome-extension.js

@@ -90,7 +90,7 @@ const injectContentScripts = function (manifest) {
     return {
       matches: script.matches,
       js: script.js.map(readArrayOfFiles),
-      run_at: script.run_at || 'document_idle'
+      runAt: script.run_at || 'document_idle'
     }
   }
 

lib/renderer/content-scripts-injector.js

@@ -0,0 +1,35 @@
+const preferences = process.getRenderProcessPreferences()
+if (!preferences || preferences.length == 0) return
+
+const {webFrame} = require('electron')
+
+// Check whether pattern matches.
+// https://developer.chrome.com/extensions/match_patterns
+const matchesPattern = function (pattern) {
+  if (pattern === '<all_urls>')
+    return true
+
+  const regexp = new RegExp('^' + pattern.replace(/\*/g, '.*') + '$')
+  return location.href.match(regexp)
+}
+
+// Run injected scripts.
+// https://developer.chrome.com/extensions/content_scripts
+const injectContentScript = function (script) {
+  for (const match of script.matches) {
+    if (!matchesPattern(match)) return
+  }
+
+  for (const js of script.js) {
+    if (script.runAt === 'document_start') {
+      webFrame.executeJavaScript(String(js))
+    }
+  }
+}
+
+// Read the renderer process preferences.
+for (const pref of preferences) {
+  if (pref.contentScripts) {
+    pref.contentScripts.forEach(injectContentScript)
+  }
+}

lib/renderer/init.js

@@ -69,6 +69,9 @@ if (window.location.protocol === 'chrome-devtools:') {
   // Override default web functions.
   require('./override')
 
+  // Inject content scripts.
+  require('./content-scripts-injector')
+
   // Load webview tag implementation.
   if (nodeIntegration === 'true' && process.guestInstanceId == null) {
     require('./web-view/web-view')