Form-associated custom elements: Update form submission logic

to match to the latest pull request [1].

- If the element has zero-length name attribute, it should not add an entry.
- The first argument of setFormValue() should be nullable, and the null
  value should add no entry.

[1] https://github.com/whatwg/html/pull/4383

Bug: 905922
Change-Id: I5bcacd633e43050e5065682043d126359bdeca7c
Reviewed-on: https://chromium-review.googlesource.com/c/1491051
Auto-Submit: Kent Tamura <tkent@chromium.org>
Commit-Queue: Hayato Ito <hayato@chromium.org>
Reviewed-by: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#635890}

third_party/blink/renderer/core/html/custom/element_internals.cc

@@ -225,14 +225,13 @@ void ElementInternals::AppendToFormData(FormData& form_data) {
     return;
   const AtomicString& name = Target().FastGetAttribute(html_names::kNameAttr);
   if (!entry_source_) {
-    if (name.IsNull())
+    if (name.IsEmpty())
       return;
     if (value_.IsFile())
       form_data.AppendFromElement(name, value_.GetAsFile());
     else if (value_.IsUSVString())
       form_data.AppendFromElement(name, value_.GetAsUSVString());
-    else
-      form_data.AppendFromElement(name, g_empty_string);
+    // Append nothing for null value.
     return;
   }
   for (const auto& entry : entry_source_->Entries()) {

third_party/blink/renderer/core/html/custom/element_internals.idl

@@ -10,7 +10,7 @@
 ]
 interface ElementInternals {
   // Attributes and operations for form-associated custom elements.
-  [RaisesException] void setFormValue(FormDataEntryValue value, optional FormData entrySource);
+  [RaisesException] void setFormValue(FormDataEntryValue? value, optional FormData entrySource);
 
   [RaisesException] readonly attribute HTMLFormElement? form;
 

third_party/blink/web_tests/custom-elements/tentative/form-submission.html

@@ -59,7 +59,7 @@ promise_test(t => {
       '<iframe name="if1"></iframe>';
   $('my-control').value = 'value-ce1';
   return submitPromise(t).then(query => {
-    assert_equals(query, '?name-pd1=value-pd1&=value-ce1&name-pd2=value-pd2');
+    assert_equals(query, '?name-pd1=value-pd1&name-pd2=value-pd2');
   });
 }, 'Single value - empty name exists');
 
@@ -76,6 +76,19 @@ promise_test(t => {
   });
 }, 'Single value - Non-empty name exists');
 
+promise_test(t => {
+  $('#container').innerHTML = '<form action="../../external/wpt/common/blank.html" target="if1">' +
+      '<input name=name-pd1 value="value-pd1">' +
+      '<my-control name="name-ce1"></my-control>' +
+      '<my-control name="name-ce2"></my-control>' +
+      '</form>' +
+      '<iframe name="if1"></iframe>';
+  $('my-control').value = null;
+  return submitPromise(t).then(query => {
+    assert_equals(query, '?name-pd1=value-pd1&name-ce2=');
+  });
+}, 'Null value should submit nothing');
+
 promise_test(t => {
   $('#container').innerHTML = '<form action="../../external/wpt/common/blank.html" target="if1">' +
       '<input name=name-pd1 value="value-pd1">' +