DevTools: [Documentation] Add signature section for renderer

Source/devtools/front_end/documentationView.css

 /*
  * 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.
  */
 
 .documentation-example-code {
     border: 1px dotted black;
     border-radius: 6px;
     padding: 1em;
@@ skipping 46 matching lines @@
 }
 
 .documentation-parameter-data-type {
     margin-right: 0.5em;
 }
 
 .documentation-parameter-optional {
     padding: 0.7ex;
     background-color: rgb(219, 234, 249);
     text-decoration: none;
-    margin-left: 1ex;
-    margin-top: -0.5ex;
     border-radius: 5px;
 }
 
 .documentation-parameter-data-type-value {
-    margin-right: 0.5em;
     padding: 0.7ex;
     background-color: rgb(254, 254, 202);
     text-decoration: none;
-    margin-left: 1ex;
-    margin-top: -0.5ex;
     border-radius: 5px;
 }
 
+.documentation-parameter-margin {
+    margin-left: 1ex;
+    margin-top: -0.5ex;
+}
+
 .documentation-parameter-name {
     font-size: 115%;
     font-style: italic;
 }
 
+.documentation-return-type {
+    padding: 0.7ex;
+    background-color: rgb(213, 255, 212);
+    text-decoration: none;
+    border-radius: 5px;
+}
+
 .documentation-page-title {
     font-size: 160%;
     font-weight: bold;
     padding-bottom: 0.7em;
 }
 
 .documentation-view {
     -webkit-user-select: text;
     padding: 1em;
 }
 
 .documentation-example-description-section {
     margin-bottom: 1em;
 }
 
 .documentation-example-link {
     float: right;
     padding: 0.7ex;
     background-color: rgb(241, 246, 251);
     text-decoration: none;
     margin-left: 1ex;
     margin-top: -0.5ex;
     border-radius: 5px;
 }