Fix BrowserAccessibility::IsLeaf to consider a node's child tree

1. https://chromium-review.googlesource.com/2171436 introduced a change
   to how `AXPlatformNodeBase::IsLeaf` works; previously, a node would
   start by querying `AXPlatformNodeBase::GetChildCount` (which relies
   on `BrowserAccessibility::PlatformChildCount`) to check whether the
   node has no children (which would make it a leaf by definition).

   After CL 2171436, `AXPlatformNodeBase::IsLeaf` is delegated to
   `BrowserAccessibility::PlatformIsLeaf`, but the case of an '<iframe>'
   is mishandled since now we don't check if the node has a child tree.

   Fixing `BrowserAccessibility::IsLeaf` to check for the child tree of
   a node; this will allow several `BrowserAccessibilityPosition`'s
   methods to correctly traverse into '<iframe>' elements.

2. Introducing a content browser test to validate that methods from
   `BrowserAccessibilityPosition` can navigate into iframes.

3. Rebaselining `DumpAccessibilityTreeTest.AccessibilityIframe` which
   incorrectly expected '<iframe>' nodes to be treated as leaves.

Bug: 1101480
Change-Id: Ib364ee78a39ef6b7854fc41985bd059dfced8a46
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2364049Reviewed-by: Kurt Catti-Schmidt <kschmi@microsoft.com>
Reviewed-by: Nektarios Paisios <nektar@chromium.org>
Commit-Queue: Ethan Jimenez <ethavar@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#800321}

content/browser/accessibility/ax_platform_node_win_browsertest.cc

@@ -604,4 +604,74 @@ IN_PROC_BROWSER_TEST_F(AXPlatformNodeWinBrowserTest,
   }
 }
 
+IN_PROC_BROWSER_TEST_F(AXPlatformNodeWinBrowserTest, IFrameTraversal) {
+  LoadInitialAccessibilityTreeFromHtmlFilePath(
+      "/accessibility/html/iframe-traversal.html");
+  WaitForAccessibilityTreeToContainNodeWithName(shell()->web_contents(),
+                                                "Text in iframe");
+
+  BrowserAccessibility* root_node = GetRootAndAssertNonNull();
+  BrowserAccessibility* before_iframe_node =
+      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_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_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_NE(nullptr, after_iframe_node);
+  ASSERT_EQ(ax::mojom::Role::kInlineTextBox, after_iframe_node->GetRole());
+
+  EXPECT_LT(*before_iframe_node->CreatePositionAt(0),
+            *inside_iframe_node->CreatePositionAt(0));
+  EXPECT_EQ(*before_iframe_node->CreatePositionAt(13),
+            *inside_iframe_node->CreatePositionAt(0));
+  EXPECT_LT(*inside_iframe_node->CreatePositionAt(0),
+            *after_iframe_node->CreatePositionAt(0));
+  EXPECT_EQ(*inside_iframe_node->CreatePositionAt(14),
+            *after_iframe_node->CreatePositionAt(0));
+
+  // Traverse the leaves of the AXTree forwards.
+  BrowserAccessibilityPosition::AXPositionInstance tree_position =
+      root_node->CreatePositionAt(0)->CreateNextLeafTreePosition();
+  EXPECT_TRUE(tree_position->IsTreePosition());
+  EXPECT_EQ(before_iframe_node, tree_position->GetAnchor());
+  tree_position = tree_position->CreateNextLeafTreePosition();
+  EXPECT_TRUE(tree_position->IsTreePosition());
+  EXPECT_EQ(inside_iframe_node, tree_position->GetAnchor());
+  tree_position = tree_position->CreateNextLeafTreePosition();
+  EXPECT_TRUE(tree_position->IsTreePosition());
+  EXPECT_EQ(after_iframe_node, tree_position->GetAnchor());
+  tree_position = tree_position->CreateNextLeafTreePosition();
+  EXPECT_TRUE(tree_position->IsNullPosition());
+
+  // Traverse the leaves of the AXTree backwards.
+  tree_position = after_iframe_node->CreatePositionAt(0)
+                      ->CreatePositionAtEndOfAnchor()
+                      ->AsLeafTreePosition();
+  EXPECT_TRUE(tree_position->IsTreePosition());
+  EXPECT_EQ(after_iframe_node, tree_position->GetAnchor());
+  tree_position = tree_position->CreatePreviousLeafTreePosition();
+  EXPECT_TRUE(tree_position->IsTreePosition());
+  EXPECT_EQ(inside_iframe_node, tree_position->GetAnchor());
+  tree_position = tree_position->CreatePreviousLeafTreePosition();
+  EXPECT_TRUE(tree_position->IsTreePosition());
+  EXPECT_EQ(before_iframe_node, tree_position->GetAnchor());
+  tree_position = tree_position->CreatePreviousLeafTreePosition();
+  EXPECT_TRUE(tree_position->IsNullPosition());
+}
+
 }  // namespace content

content/browser/accessibility/browser_accessibility.cc

@@ -124,13 +124,9 @@ ui::AXPlatformNode* BrowserAccessibility::GetAXPlatformNode() const {
 }
 
 uint32_t BrowserAccessibility::PlatformChildCount() const {
-  if (HasStringAttribute(ax::mojom::StringAttribute::kChildTreeId)) {
-    if (PlatformGetRootOfChildTree())
-      return 1;
+  if (PlatformIsLeaf())
     return 0;
-  }
-
-  return PlatformIsLeaf() ? 0 : InternalChildCount();
+  return PlatformGetRootOfChildTree() ? 1 : InternalChildCount();
 }
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetParent() const {
@@ -146,10 +142,8 @@ BrowserAccessibility* BrowserAccessibility::PlatformGetFirstChild() const {
 }
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetLastChild() const {
-  BrowserAccessibility* last_unignored_child = InternalGetLastChild();
-  if (!last_unignored_child)
-    last_unignored_child = PlatformGetRootOfChildTree();
-  return last_unignored_child;
+  BrowserAccessibility* child_tree_root = PlatformGetRootOfChildTree();
+  return child_tree_root ? child_tree_root : InternalGetLastChild();
 }
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetNextSibling() const {
@@ -209,20 +203,12 @@ bool BrowserAccessibility::IsLineBreakObject() const {
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetChild(
     uint32_t child_index) const {
-  BrowserAccessibility* result = nullptr;
-
-  if (HasStringAttribute(ax::mojom::StringAttribute::kChildTreeId)) {
-    DCHECK_EQ(node_->children().size(), 0u)
-        << "A node should not have both children and a child tree.";
-
-    // child_trees do not have siblings.
-    if (child_index == 0)
-      result = PlatformGetRootOfChildTree();
-  } else {
-    result = InternalGetChild(child_index);
+  BrowserAccessibility* child_tree_root = PlatformGetRootOfChildTree();
+  if (child_tree_root) {
+    // A node with a child tree has only one child.
+    return child_index ? nullptr : child_tree_root;
   }
-
-  return result;
+  return InternalGetChild(child_index);
 }
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetClosestPlatformObject()
@@ -1553,7 +1539,7 @@ bool BrowserAccessibility::IsLeaf() const {
     return !child_count ||
            (child_count == 1 && InternalGetFirstChild()->IsText());
   }
-  return node()->IsLeaf();
+  return PlatformGetRootOfChildTree() ? false : node()->IsLeaf();
 }
 
 bool BrowserAccessibility::IsToplevelBrowserWindow() {
@@ -2145,15 +2131,18 @@ bool BrowserAccessibility::SetHypertextSelection(int start_offset,
 }
 
 BrowserAccessibility* BrowserAccessibility::PlatformGetRootOfChildTree() const {
-  if (!HasStringAttribute(ax::mojom::StringAttribute::kChildTreeId))
+  std::string child_tree_id;
+  if (!GetStringAttribute(ax::mojom::StringAttribute::kChildTreeId,
+                          &child_tree_id)) {
     return nullptr;
-  AXTreeID child_tree_id = AXTreeID::FromString(
-      GetStringAttribute(ax::mojom::StringAttribute::kChildTreeId));
+  }
+  DCHECK_EQ(node_->children().size(), 0u)
+      << "A node should not have both children and a child tree.";
+
   BrowserAccessibilityManager* child_manager =
-      BrowserAccessibilityManager::FromID(child_tree_id);
+      BrowserAccessibilityManager::FromID(AXTreeID::FromString(child_tree_id));
   if (child_manager && child_manager->GetRoot()->PlatformGetParent() == this)
     return child_manager->GetRoot();
-
   return nullptr;
 }
 

content/test/data/accessibility/html/iframe-expected-win.txt

 ROLE_SYSTEM_DOCUMENT parent='ROLE_SYSTEM_WINDOW' window_class='Chrome_RenderWidgetHostHWND' READONLY FOCUSABLE ia2_hypertext='<obj0>'
 ++IA2_ROLE_SECTION parent='ROLE_SYSTEM_DOCUMENT' window_class='Chrome_RenderWidgetHostHWND' ia2_hypertext='<obj0>'
-++++IA2_ROLE_INTERNAL_FRAME name='Empty iframe' parent='ROLE_SYSTEM_GROUPING' window_class='Chrome_RenderWidgetHostHWND'
+++++IA2_ROLE_INTERNAL_FRAME name='Empty iframe' parent='ROLE_SYSTEM_GROUPING' window_class='Chrome_RenderWidgetHostHWND' ia2_hypertext='<obj0>'
 ++++++ROLE_SYSTEM_DOCUMENT parent='ROLE_SYSTEM_DOCUMENT' window_class='Chrome_RenderWidgetHostHWND' READONLY FOCUSABLE
\ No newline at end of file

content/test/data/accessibility/html/iframe-traversal.html

+<!--
+@WIN-ALLOW:ia2_hypertext=*
+-->
+<!DOCTYPE html>
+<html>
+<body>
+<p>Before iframe</p>
+<div>
+  <iframe src="/accessibility/html/frame/static_text.html">
+  </iframe>
+</div>
+<p>After iframe</p>
+</body>
+</html>