Remove the allow-displaying-mixed-content setting from Blink.

components/test_runner/test_preferences.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/test_runner/test_preferences.h"
 
 #include "build/build_config.h"
 
 using blink::WebSettings;
 using blink::WebString;
 
 namespace test_runner {
 
 TestPreferences::TestPreferences() { Reset(); }
 
 void TestPreferences::Reset() {
   default_font_size = 16;
   minimum_font_size = 0;
   xss_auditor_enabled = false;
-  allow_display_of_insecure_content = true;
   allow_file_access_from_file_urls = true;
   allow_running_of_insecure_content = true;
   default_text_encoding_name = WebString::fromUTF8("ISO-8859-1");
   experimental_webgl_enabled = false;
   experimental_css_grid_layout_enabled = true;
   java_script_can_access_clipboard = true;
   java_script_can_open_windows_automatically = true;
   supports_multiple_windows = true;
   java_script_enabled = true;
   loads_images_automatically = true;
@@ skipping 15 matching lines @@
   should_respect_image_orientation = false;
   asynchronous_spell_checking_enabled = false;
   web_security_enabled = true;
   disable_reading_from_canvas = false;
   strict_mixed_content_checking = false;
   strict_powerful_feature_restrictions = false;
   spatial_navigation_enabled = false;
 }
 
 }  // namespace test_runner