Fix facebook_credentials_backend_unittest on android-content-shell.

tools/telemetry/telemetry/facebook_credentials_backend.py

Index: tools/telemetry/telemetry/facebook_credentials_backend.py
diff --git a/tools/telemetry/telemetry/facebook_credentials_backend.py b/tools/telemetry/telemetry/facebook_credentials_backend.py
index dc4219a7900123a9c7864d4e1dd6b6b78c5930c7..59a36651fb92261995f73738e1c60fb079c7f805 100644
--- a/tools/telemetry/telemetry/facebook_credentials_backend.py
+++ b/tools/telemetry/telemetry/facebook_credentials_backend.py
@@ -6,6 +6,11 @@ from telemetry import form_based_credentials_backend
 
 class FacebookCredentialsBackend(
     form_based_credentials_backend.FormBasedCredentialsBackend):
+  def IsAlreadyLoggedIn(self, tab):
+    return tab.EvaluateJavaScript(
+        'document.getElementById("fbNotificationsList")!== null || '
+        'document.getElementById("m_home_notice")!== null')
+
   @property
   def credentials_type(self):
     return 'facebook'
@@ -19,10 +24,6 @@ class FacebookCredentialsBackend(
     return 'login_form'
 
   @property
-  def already_logged_in_element_id(self):
-    return 'fbNotificationsList'
-
-  @property
   def login_input_id(self):
     return 'email'