[chromedriver] Fallback to devtools for screenshotting of forbidden urls.

chrome/test/chromedriver/extension/background.js

Index: chrome/test/chromedriver/extension/background.js
diff --git a/chrome/test/chromedriver/extension/background.js b/chrome/test/chromedriver/extension/background.js
index 16ea857d1542de4dd13a14999b59eff04f43d480..9158d6f5d72672bafc3bf7260cfe83d7771ebddb 100644
--- a/chrome/test/chromedriver/extension/background.js
+++ b/chrome/test/chromedriver/extension/background.js
@@ -27,6 +27,13 @@ function checkForExtensionError(errCallback) {
  */
 function captureScreenshot(callback, errCallback) {
   chrome.tabs.captureVisibleTab({format:'png'}, function(dataUrl) {
+    if (chrome.extension.lastError &&
+        chrome.extension.lastError.message.indexOf('permission') != -1) {
+      var error = new Error(chrome.extension.lastError.message);
+      error.code = 103;  // kForbidden
+      errCallback(error);
+      return;
+    }
     checkForExtensionError(errCallback);
     var base64 = ';base64,';
     callback(dataUrl.substr(dataUrl.indexOf(base64) + base64.length))