Ensure BrowserAccessibility::Platform* methods have the same children

BrowserAccessibility::PlatformChildCount
considers BrowserAccessibility::IsLeaf() as having 0 children

while

BrowserAccessibility::PlatformGetFirstChild (via BrowserAccessibility::PlatformGetChild)
BrowserAccessibility::PlatformGetLastChild

do not.

Make this consistent by having Platform[First|Last]Child check that
PlatformChildCount is 0 and return nullptr accordingly.

Change-Id: I81d1535bf658642ed9f6c8dc9e7f00a5ba38bdd4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3574854
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Commit-Queue: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#991087}

content/browser/accessibility/ax_platform_node_win_browsertest.cc

@@ -726,23 +726,32 @@ IN_PROC_BROWSER_TEST_F(AXPlatformNodeWinBrowserTest, IFrameTraversal) {
       FindNodeAfter(root_node, "Before iframe");
   ASSERT_NE(nullptr, before_iframe_node);
   ASSERT_EQ(ax::mojom::Role::kStaticText, before_iframe_node->GetRole());
-  before_iframe_node = before_iframe_node->PlatformGetFirstChild();
+
+  ASSERT_EQ(0U, before_iframe_node->PlatformChildCount());
+  ASSERT_EQ(1U, before_iframe_node->InternalChildCount());
+  before_iframe_node = before_iframe_node->InternalGetFirstChild();
   ASSERT_NE(nullptr, before_iframe_node);
   ASSERT_EQ(ax::mojom::Role::kInlineTextBox, before_iframe_node->GetRole());
 
   BrowserAccessibility* inside_iframe_node =
       FindNodeAfter(before_iframe_node, "Text in iframe");
   ASSERT_NE(nullptr, inside_iframe_node);
   ASSERT_EQ(ax::mojom::Role::kStaticText, inside_iframe_node->GetRole());
-  inside_iframe_node = inside_iframe_node->PlatformGetFirstChild();
+
+  ASSERT_EQ(0U, inside_iframe_node->PlatformChildCount());
+  ASSERT_EQ(1U, inside_iframe_node->InternalChildCount());
+  inside_iframe_node = inside_iframe_node->InternalGetFirstChild();
   ASSERT_NE(nullptr, inside_iframe_node);
   ASSERT_EQ(ax::mojom::Role::kInlineTextBox, inside_iframe_node->GetRole());
 
   BrowserAccessibility* after_iframe_node =
       FindNodeAfter(inside_iframe_node, "After iframe");
   ASSERT_NE(nullptr, after_iframe_node);
   ASSERT_EQ(ax::mojom::Role::kStaticText, after_iframe_node->GetRole());
-  after_iframe_node = after_iframe_node->PlatformGetFirstChild();
+
+  ASSERT_EQ(0U, after_iframe_node->PlatformChildCount());
+  ASSERT_EQ(1U, after_iframe_node->InternalChildCount());
+  after_iframe_node = after_iframe_node->InternalGetFirstChild();
   ASSERT_NE(nullptr, after_iframe_node);
   ASSERT_EQ(ax::mojom::Role::kInlineTextBox, after_iframe_node->GetRole());
 

content/browser/accessibility/browser_accessibility.cc

@@ -163,10 +163,16 @@ BrowserAccessibility* BrowserAccessibility::PlatformGetParent() const {
 }
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetFirstChild() const {
+  if (PlatformChildCount() == 0)
+    return nullptr;
+
   return PlatformGetChild(0);
 }
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetLastChild() const {
+  if (PlatformChildCount() == 0)
+    return nullptr;
+
   BrowserAccessibility* child_tree_root = PlatformGetRootOfChildTree();
   return child_tree_root ? child_tree_root : InternalGetLastChild();
 }
@@ -211,6 +217,9 @@ bool BrowserAccessibility::IsLineBreakObject() const {
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetChild(
     uint32_t child_index) const {
+  if (PlatformChildCount() == 0)
+    return nullptr;
+
   BrowserAccessibility* child_tree_root = PlatformGetRootOfChildTree();
   if (child_tree_root) {
     // A node with a child tree has only one child.
@@ -776,11 +785,6 @@ gfx::RectF BrowserAccessibility::GetInlineTextRect(const int start_offset,
 
 BrowserAccessibility* BrowserAccessibility::ApproximateHitTest(
     const gfx::Point& blink_screen_point) {
-  // TODO(accessibility): propagate this to all tree traversal methods and
-  // remove here. This keeps things equivalent for now.
-  if (IsLeaf())
-    return this;
-
   // The best result found that's a child of this object.
   BrowserAccessibility* child_result = nullptr;
   // The best result that's an indirect descendant like grandchild, etc.

content/browser/accessibility/browser_accessibility_manager_auralinux_unittest.cc

@@ -103,13 +103,17 @@ TEST_F(BrowserAccessibilityManagerAuraLinuxTest, TestEmitChildrenChanged) {
                    }),
                    nullptr);
 
+  // The static text is a platform leaf.
+  ASSERT_EQ(0U, static_text_accessible->PlatformChildCount());
+  ASSERT_EQ(1U, static_text_accessible->InternalChildCount());
+
   BrowserAccessibility* inline_text_accessible =
-      static_text_accessible->PlatformGetChild(0);
+      static_text_accessible->InternalGetChild(0);
   // PlatformLeaf node such as InlineText should not trigger
   // 'children-changed' event to the parent when subtree is changed.
   aura_linux_manager->FireSubtreeCreatedEvent(inline_text_accessible);
   aura_linux_manager->OnSubtreeWillBeDeleted(manager->ax_tree(),
                                              inline_text_accessible->node());
 }
 
-}  // namespace content
+}  // namespace content

content/browser/accessibility/browser_accessibility_manager_unittest.cc

@@ -937,8 +937,11 @@ TEST_F(BrowserAccessibilityManagerTest, TestFindIndicesInCommonParent) {
   ASSERT_EQ(2U, div_accessible->PlatformChildCount());
   BrowserAccessibility* button_accessible = div_accessible->PlatformGetChild(0);
   ASSERT_NE(nullptr, button_accessible);
+  ASSERT_EQ(0U, button_accessible->PlatformChildCount());
+  ASSERT_EQ(1U, button_accessible->InternalChildCount());
+
   BrowserAccessibility* button_text_accessible =
-      button_accessible->PlatformGetChild(0);
+      button_accessible->InternalGetChild(0);
   ASSERT_NE(nullptr, button_text_accessible);
   BrowserAccessibility* line_break_accessible =
       div_accessible->PlatformGetChild(1);
@@ -1096,8 +1099,11 @@ TEST_F(BrowserAccessibilityManagerTest, TestGetTextForRange) {
   ASSERT_EQ(3U, div_accessible->PlatformChildCount());
   BrowserAccessibility* button_accessible = div_accessible->PlatformGetChild(0);
   ASSERT_NE(nullptr, button_accessible);
+  ASSERT_EQ(0U, button_accessible->PlatformChildCount());
+  ASSERT_EQ(1U, button_accessible->InternalChildCount());
+
   BrowserAccessibility* button_text_accessible =
-      button_accessible->PlatformGetChild(0);
+      button_accessible->InternalGetChild(0);
   ASSERT_NE(nullptr, button_text_accessible);
   BrowserAccessibility* container_accessible =
       div_accessible->PlatformGetChild(1);

content/browser/accessibility/browser_accessibility_unittest.cc

@@ -960,11 +960,18 @@ TEST_F(BrowserAccessibilityTest, CreatePositionAt) {
   BrowserAccessibility::AXPosition pos = gc_accessible->CreatePositionAt(0);
   EXPECT_TRUE(pos->IsTreePosition());
 
+  ASSERT_EQ(1U, gc_accessible->InternalChildCount());
+#if BUILDFLAG(IS_ANDROID)
+  // On Android, nodes with only static text can drop their children.
+  ASSERT_EQ(0U, gc_accessible->PlatformChildCount());
+#else
+  ASSERT_EQ(1U, gc_accessible->PlatformChildCount());
   BrowserAccessibility* text_accessible = gc_accessible->PlatformGetChild(0);
   ASSERT_NE(nullptr, text_accessible);
 
   pos = text_accessible->CreatePositionAt(0);
   EXPECT_TRUE(pos->IsTextPosition());
+#endif  // BUILDFLAG(IS_ANDROID)
 }
 
 }  // namespace content