Don't use plugin-specific content settings that are from user prefs

chrome/browser/plugins/plugin_utils.cc

 // Copyright 2016 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 "chrome/browser/plugins/plugin_utils.h"
 
 #include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 #include "components/content_settings/core/browser/host_content_settings_map.h"
 #include "content/public/common/webplugininfo.h"
@@ skipping 54 matching lines @@
     content_settings::SettingInfo specific_info;
     std::unique_ptr<base::Value> specific_setting =
         host_content_settings_map->GetWebsiteSetting(
             policy_url, plugin_url, CONTENT_SETTINGS_TYPE_PLUGINS, resource,
             &specific_info);
     content_settings::SettingInfo general_info;
     std::unique_ptr<base::Value> general_setting =
         host_content_settings_map->GetWebsiteSetting(
             policy_url, plugin_url, CONTENT_SETTINGS_TYPE_PLUGINS,
             std::string(), &general_info);
-    // If there is a plugin-specific setting, we use it, unless the general
-    // setting was set by policy, in which case it takes precedence.
+    // The order of precedence is:
+    // -If a general setting was set by policy, use it.
+    // -If there is a plugin-specific setting which is not user provided (e.g.
+    //  it comes from an extension or some other source), use it. We don't use
+    //  user-provided plugin-specific settings because there is no longer any UI
+    //  to set them.
+    // -Otherwise use the general setting.
     uses_plugin_specific_setting =
         specific_setting &&
+        specific_info.source != content_settings::SETTING_SOURCE_USER &&
         general_info.source != content_settings::SETTING_SOURCE_POLICY;
     if (uses_plugin_specific_setting) {
       value = std::move(specific_setting);
       info = specific_info;
     } else {
       value = std::move(general_setting);
       info = general_info;
     }
   }
   *setting = content_settings::ValueToContentSetting(value.get());
@@ skipping 29 matching lines @@
 ContentSetting PluginUtils::GetFlashPluginContentSetting(
     const HostContentSettingsMap* host_content_settings_map,
     const GURL& policy_url,
     const GURL& plugin_url) {
   ContentSetting plugin_setting = CONTENT_SETTING_DEFAULT;
   GetPluginContentSettingInternal(
       host_content_settings_map, false /* use_javascript_setting */, policy_url,
       plugin_url, kFlashPluginID, &plugin_setting, nullptr, nullptr);
   return plugin_setting;
 }