Auto merge of #19461 - jonleighton:issue-19171-4, r=KiChjang

Handle cases where selection API doesn't apply

The selection API only applies to certain <input> types:

https://html.spec.whatwg.org/multipage/#do-not-apply

This commit ensures that we handle that correctly.

Some notes:

1. TextControl::set_dom_selection_direction now calls
   set_selection_range(), which means that setting selectionDirection will
   now fire a selection event, as it should per the spec.

2. There is a test for the firing of the select event in
   tests/wpt/web-platform-tests/html/semantics/forms/textfieldselection/select-event.html,
   however the test did not run due to this syntax error:

   (pid:26017) "ERROR:script::dom::bindings::error: Error at http://web-platform.test:8000/html/semantics/forms/textfieldselection/select-event.html:50:11 missing = in const declaration"

   This happens due to the us of the "for (const foo of ...)" construct.
   Per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of
   this should actually work, so it's somewhat unsatisfying to have to
   change the test.

3. I removed tests/wpt/web-platform-tests/html/semantics/forms/textfieldselection/selection-not-application-textarea.html
   because it doesn't seem to add any extra value - the selection API
   always applies to textarea elements, and the API is tested elsewhere.

4. If an `<input>`'s type is unset, it defaults to a text, and the
   selection API applies. Also, if an `<input>`'s type is set to an
   invalid value, it defaults to a text too. This second case doesn't
   currently work, and I'll need to do more restructuring of the code in
   a future commit. See discussion with nox in IRC:
   https://mozilla.logbot.info/servo/20171201#c13946454-c13946594

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components/script/dom/htmlinputelement.rs

@@ -405,6 +405,18 @@ impl TextControl for HTMLInputElement {
     fn textinput(&self) -> &DomRefCell<TextInput<ScriptToConstellationChan>> {
         &self.textinput
     }
+
+    // https://html.spec.whatwg.org/multipage/#concept-input-apply
+    fn selection_api_applies(&self) -> bool {
+        match self.input_type() {
+            InputType::Text | InputType::Search | InputType::Url
+            | InputType::Tel | InputType::Password => {
+                true
+            },
+
+            _ => false
+        }
+    }
 }
 
 impl HTMLInputElementMethods for HTMLInputElement {
@@ -676,38 +688,38 @@ impl HTMLInputElementMethods for HTMLInputElement {
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-textarea/input-selectionstart
-    fn SelectionStart(&self) -> u32 {
-        self.dom_selection_start()
+    fn GetSelectionStart(&self) -> Option<u32> {
+        self.get_dom_selection_start()
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-textarea/input-selectionstart
-    fn SetSelectionStart(&self, start: u32) {
-        self.set_dom_selection_start(start);
+    fn SetSelectionStart(&self, start: Option<u32>) -> ErrorResult {
+        self.set_dom_selection_start(start)
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-textarea/input-selectionend
-    fn SelectionEnd(&self) -> u32 {
-        self.dom_selection_end()
+    fn GetSelectionEnd(&self) -> Option<u32> {
+        self.get_dom_selection_end()
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-textarea/input-selectionend
-    fn SetSelectionEnd(&self, end: u32) {
+    fn SetSelectionEnd(&self, end: Option<u32>) -> ErrorResult {
         self.set_dom_selection_end(end)
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-textarea/input-selectiondirection
-    fn SelectionDirection(&self) -> DOMString {
-        self.dom_selection_direction()
+    fn GetSelectionDirection(&self) -> Option<DOMString> {
+        self.get_dom_selection_direction()
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-textarea/input-selectiondirection
-    fn SetSelectionDirection(&self, direction: DOMString) {
-        self.set_dom_selection_direction(direction);
+    fn SetSelectionDirection(&self, direction: Option<DOMString>) -> ErrorResult {
+        self.set_dom_selection_direction(direction)
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-textarea/input-setselectionrange
-    fn SetSelectionRange(&self, start: u32, end: u32, direction: Option<DOMString>) {
-        self.set_dom_selection_range(start, end, direction);
+    fn SetSelectionRange(&self, start: u32, end: u32, direction: Option<DOMString>) -> ErrorResult {
+        self.set_dom_selection_range(start, end, direction)
     }
 
     // Select the files based on filepaths passed in,