DevTools: [SSP] Implement adding new rule in user stylesheet

LayoutTests/inspector-protocol/css/css-create-stylesheet-and-add-rule-expected.txt

 Inspected contents
 Style sheet added: regular (stylesheet.css)
 Dumping matched rules: 
 *#inspected* {    regular
     color: red;
 }
 Adding a rule to the existing stylesheet.
+==== Style sheet text ====
+#inspected {}#inspected {
+    color: red;
+}
 Dumping matched rules: 
 *#inspected* {    regular
-    color: red;
 }
 *#inspected* {    regular
+    color: red;
 }
 Creating inspector stylesheet.
 Style sheet added: inspector
 Adding a rule to the inspector stylesheet.
+==== Style sheet text ====
+#inspected {}
 Dumping matched rules: 
 *#inspected* {    regular
+}
+*#inspected* {    regular
     color: red;
 }
-*#inspected* {    regular
-}
 *#inspected* {    inspector
 }