Auto merge of #10834 - yoava333:master, r=SimonSapin

added support for :read-only and :read-write pseudo-classes

partial fix for https://github.com/servo/servo/issues/10732

It's not a full fix because:
1. there's a bug in wpt-test https://github.com/w3c/web-platform-tests/issues/2889#issuecomment-214144420
2. we don't fully support all input types (namely image, color, hidden and range), which are defaulted to input text. this means that :read-write which is applicable to input text is mis-handled in those cases.
3. we don't support contenteditable, which is also possibly :read-write

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components/layout/wrapper.rs

@@ -550,13 +550,17 @@ impl<'le> ::selectors::Element for ServoLayoutElement<'le> {
                 }
             },
 
+            NonTSPseudoClass::ReadOnly =>
+                !self.element.get_state_for_layout().contains(pseudo_class.state_flag()),
+
             NonTSPseudoClass::Active |
             NonTSPseudoClass::Focus |
             NonTSPseudoClass::Hover |
             NonTSPseudoClass::Enabled |
             NonTSPseudoClass::Disabled |
             NonTSPseudoClass::Checked |
-            NonTSPseudoClass::Indeterminate =>
+            NonTSPseudoClass::Indeterminate |
+            NonTSPseudoClass::ReadWrite =>
                 self.element.get_state_for_layout().contains(pseudo_class.state_flag())
         }
     }