[A11y] Use title value when the input type image with empty alt and

non-empty title

At the discussion[1], in case of the `img` element, it is written to use
the alt even if it is an empty string explicitly. But in case of alt of
input type=image, there is no explicit description of empty value. So
like aria-label and aria-labelledby, it was understood that if it has
an empty value, it allows a meaningful value in the next step to be used.

Therefore, the `title` value has been changed to be used as accessible
name, according to the accessible name computation algorithm[2], when
the `alt` attribute does not provide a meaningful value.

[1]: w3c/html-aam#414
[2]: https://www.w3.org/TR/html-aam-1.0/#img-element-accessible-name-computation

Signed-off-by: Hunseop Jeong <[email protected]>
Bug: 1342873
Change-Id: Ifc7dfcd22897f0a59943c2330b5808afb494f889
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4700003
Reviewed-by: Aaron Leventhal <[email protected]>
Commit-Queue: Aaron Leventhal <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1177870}

third_party/blink/renderer/modules/accessibility/ax_node_object.cc

@@ -5493,7 +5493,7 @@ String AXNodeObject::NativeTextAlternative(
       name_sources->push_back(NameSource(*found_text_alternative, kAltAttr));
       name_sources->back().type = name_from;
     }
-    if (!alt.IsNull()) {
+    if (!alt.empty() && !alt.IsNull()) {
       text_alternative = alt;
       if (name_sources) {
         NameSource& source = name_sources->back();

third_party/blink/web_tests/accessibility/name-calc-native-markup-input-buttons.html

@@ -221,3 +221,15 @@
     assert_equals(axImageInput5.nameFrom, "title");
 }, "Image input with title only");
 </script>
+
+<div class="container">
+    <input id="image-input6" type="image" src="resources/cake.png" alt="" title="image-input-title6">
+</div>
+
+<script>
+test(function(t) {
+    var axImageInput6 = accessibilityController.accessibleElementById("image-input6");
+    assert_equals(axImageInput6.name, "image-input-title6");
+    assert_equals(axImageInput6.nameFrom, "title");
+}, "Image input with empty alt and title");
+</script>