Guard flag CSSAtRuleCounterStyle properly in AXLayoutObject::GetListStyle

A previous patch crrev.com/c/2629991 has a bug that it always enters a
code path that should be entered only when CSSAtRuleCounterStyle is
enabled.

This patch handles the flag properly.

Bug: 1167596
Change-Id: I15dcdae0d70a716185e5ab376a0c08bcb5f134dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2636378
Auto-Submit: Xiaocheng Hu <xiaochengh@chromium.org>
Commit-Queue: Nektarios Paisios <nektar@chromium.org>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844767}

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

@@ -914,7 +914,8 @@ ax::mojom::blink::ListStyle AXLayoutObject::GetListStyle() const {
       if (counter_style_name == "decimal-leading-zero") {
         // 'decimal-leading-zero' may be overridden by custom counter styles. We
         // return kNumeric only when we are using the predefined counter style.
-        if (&ListMarker::GetCounterStyle(*GetDocument(), *computed_style) ==
+        if (!RuntimeEnabledFeatures::CSSAtRuleCounterStyleEnabled() ||
+            &ListMarker::GetCounterStyle(*GetDocument(), *computed_style) ==
                 &CounterStyleMap::GetUACounterStyleMap()
                      ->FindCounterStyleAcrossScopes("decimal-leading-zero"))
           return ax::mojom::blink::ListStyle::kNumeric;

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

@@ -166,4 +166,54 @@ TEST_F(AXLayoutObjectTest, AccessibilityHitTestShadowDOM) {
   run_test(ShadowRootType::kClosed);
 }
 
+// https://crbug.com/1167596
+TEST_F(AXLayoutObjectTest, GetListStyleDecimalLeadingZero) {
+  ScopedCSSAtRuleCounterStyleForTest scope(false);
+
+  using ListStyle = ax::mojom::blink::ListStyle;
+
+  SetBodyInnerHTML(R"HTML(
+  <ul>
+    <li id="target" style="list-style-type: decimal-leading-zero"></li>
+  </ul>
+  )HTML");
+
+  EXPECT_EQ(ListStyle::kNumeric,
+            GetAXObjectByElementId("target")->GetListStyle());
+}
+
+// https://crbug.com/1167596
+TEST_F(AXLayoutObjectTest, GetListStyleDecimalLeadingZeroAsCustomCounterStyle) {
+  ScopedCSSAtRuleCounterStyleForTest scope(true);
+
+  using ListStyle = ax::mojom::blink::ListStyle;
+
+  SetBodyInnerHTML(R"HTML(
+  <ul>
+    <li id="target" style="list-style-type: decimal-leading-zero"></li>
+  </ul>
+  )HTML");
+
+  EXPECT_EQ(ListStyle::kNumeric,
+            GetAXObjectByElementId("target")->GetListStyle());
+}
+// https://crbug.com/1167596
+TEST_F(AXLayoutObjectTest, GetListStyleOverriddenDecimalLeadingZero) {
+  ScopedCSSAtRuleCounterStyleForTest scope(true);
+
+  using ListStyle = ax::mojom::blink::ListStyle;
+
+  SetBodyInnerHTML(R"HTML(
+  <style>
+  @counter-style decimal-leading-zero { system: extends upper-roman; }
+  </style>
+  <ul>
+    <li id="target" style="list-style-type: decimal-leading-zero"></li>
+  </ul>
+  )HTML");
+
+  EXPECT_EQ(ListStyle::kOther,
+            GetAXObjectByElementId("target")->GetListStyle());
+}
+
 }  // namespace blink