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/style/element_state.rs

@@ -27,5 +27,7 @@ bitflags! {
         const IN_CHECKED_STATE = 0x20,
         #[doc = "https://html.spec.whatwg.org/multipage/#selector-indeterminate"]
         const IN_INDETERMINATE_STATE = 0x40,
+        #[doc = "https://html.spec.whatwg.org/multipage/#selector-read-write"]
+        const IN_READ_WRITE_STATE = 0x80,
     }
 }

components/style/selector_impl.rs

@@ -44,6 +44,8 @@ pub enum NonTSPseudoClass {
     Checked,
     Indeterminate,
     ServoNonZeroBorder,
+    ReadWrite,
+    ReadOnly
 }
 
 impl NonTSPseudoClass {
@@ -58,6 +60,7 @@ impl NonTSPseudoClass {
             Disabled => IN_DISABLED_STATE,
             Checked => IN_CHECKED_STATE,
             Indeterminate => IN_INDETERMINATE_STATE,
+            ReadOnly | ReadWrite => IN_READ_WRITE_STATE,
 
             AnyLink |
             Link |
@@ -88,6 +91,8 @@ impl SelectorImpl for ServoSelectorImpl {
             "disabled" => Disabled,
             "checked" => Checked,
             "indeterminate" => Indeterminate,
+            "read-write" => ReadWrite,
+            "read-only" => ReadOnly,
             "-servo-nonzero-border" => {
                 if !context.in_user_agent_stylesheet {
                     return Err(());