Add sample extension that allows setting plugin-specific content settings.

chrome/common/extensions/docs/examples/extensions/plugin_settings/css/rule_list.css

Index: chrome/common/extensions/docs/examples/extensions/plugin_settings/css/rule_list.css
diff --git a/chrome/common/extensions/docs/examples/extensions/plugin_settings/css/rule_list.css b/chrome/common/extensions/docs/examples/extensions/plugin_settings/css/rule_list.css
new file mode 100644
index 0000000000000000000000000000000000000000..86b685ceb554ddda7849a7f258d50f9f9cb62c6f
--- /dev/null
+++ b/chrome/common/extensions/docs/examples/extensions/plugin_settings/css/rule_list.css
@@ -0,0 +1,42 @@
+/*
+Copyright (c) 2011 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.
+*/
+
+.rule-pattern {
+  -webkit-box-flex: 1;
+  -webkit-margin-end: 10px;
+  -webkit-margin-start: 14px;
+}
+
+.rule-behavior {
+  display: inline-block;
+  width: 120px;
+}
+
+select.rule-behavior {
+  vertical-align: middle;
+}
+
+.settings-list,
+.settings-list-empty {
+  border: 1px solid #d9d9d9;
+  border-radius: 2px;
+}
+
+.settings-list-empty {
+  background-color: #f4f4f4;
+  box-sizing: border-box;
+  min-height: 125px;
+  padding-left: 20px;
+  padding-top: 20px;
+}
+
+.pattern-column-header {
+  -webkit-box-flex: 1;
+}
+
+.setting-column-header {
+  width: 145px;
+}