[a11y] AXPlatformNodeAuraLinux::HitTestSync recurses into descendants

This CL allows atk_ref_accessible_at_point on the native frame or
panel to hittest web area.

According to the comment from
ViewAXPlatformNodeDelegate::HitTestSync, AXPlatformNode
is supposed to do a recursive hit test and AXPlatformNodeWin
works recursively already. So, AXPlatformNodeAuraLinux hittests
recursively.

The difference between Windows and AuraLinux is that WebArea
is also a descendant of the top window in AuraLinux.

AX-Relnotes: atk_ref_accessible_at_point recurses into descendants.
So, it finds a node from the web page when it's called on the
ancestor of web area.

Bug: 1051616
Change-Id: I03f0a37999fdaf9b2656b7eddc805467657a4b17
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2210291Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Julie Kim <jkim@igalia.com>
Cr-Commit-Position: refs/heads/master@{#773020}

content/browser/accessibility/accessibility_auralinux_browsertest.cc

@@ -1731,4 +1731,68 @@ IN_PROC_BROWSER_TEST_F(AccessibilityAuraLinuxBrowserTest,
   }
 }
 
+IN_PROC_BROWSER_TEST_F(AccessibilityAuraLinuxBrowserTest,
+                       HitTestOnAncestorOfWebRoot) {
+  // Load the page.
+  LoadInitialAccessibilityTreeFromHtml(R"HTML(
+      <button>This is a button</button>
+      )HTML");
+
+  WebContentsImpl* web_contents =
+      static_cast<WebContentsImpl*>(shell()->web_contents());
+  BrowserAccessibilityManager* manager =
+      web_contents->GetRootBrowserAccessibilityManager();
+
+  // Find a node to hit test. Note that this is a really simple page,
+  // so synchronous hit testing will work fine.
+  BrowserAccessibility* node = manager->GetRoot();
+  while (node && node->GetRole() != ax::mojom::Role::kButton)
+    node = manager->NextInTreeOrder(node);
+  DCHECK(node);
+
+  // Get the screen bounds of the hit target and find the point in the middle.
+  gfx::Rect bounds = node->GetClippedScreenBoundsRect();
+  gfx::Point point = bounds.CenterPoint();
+
+  // Get the root AXPlatformNodeAuraLinux.
+  ui::AXPlatformNodeAuraLinux* root_platform_node =
+      static_cast<ui::AXPlatformNodeAuraLinux*>(
+          ui::AXPlatformNode::FromNativeViewAccessible(
+              manager->GetRoot()->GetNativeViewAccessible()));
+
+  // First test that calling accHitTest on the root node returns the button.
+  {
+    gfx::NativeViewAccessible hit_child = root_platform_node->HitTestSync(
+        point.x(), point.y(), AtkCoordType::ATK_XY_SCREEN);
+    ASSERT_NE(nullptr, hit_child);
+    ui::AXPlatformNode* hit_child_node =
+        ui::AXPlatformNode::FromNativeViewAccessible(hit_child);
+    ASSERT_NE(nullptr, hit_child_node);
+    EXPECT_EQ(node->GetId(), hit_child_node->GetDelegate()->GetData().id);
+  }
+
+  // Now test it again, but this time caliing accHitTest on the parent
+  // IAccessible of the web root node.
+  {
+    RenderWidgetHostViewAura* rwhva = static_cast<RenderWidgetHostViewAura*>(
+        shell()->web_contents()->GetRenderWidgetHostView());
+    gfx::NativeViewAccessible ancestor = rwhva->GetParentNativeViewAccessible();
+
+    ASSERT_NE(nullptr, ancestor);
+
+    ui::AXPlatformNodeAuraLinux* ancestor_node =
+        static_cast<ui::AXPlatformNodeAuraLinux*>(
+            ui::AXPlatformNode::FromNativeViewAccessible(ancestor));
+    ASSERT_NE(nullptr, ancestor_node);
+
+    gfx::NativeViewAccessible hit_child = ancestor_node->HitTestSync(
+        point.x(), point.y(), AtkCoordType::ATK_XY_SCREEN);
+    ASSERT_NE(nullptr, hit_child);
+    ui::AXPlatformNode* hit_child_node =
+        ui::AXPlatformNode::FromNativeViewAccessible(hit_child);
+    ASSERT_NE(nullptr, hit_child_node);
+    EXPECT_EQ(node->GetId(), hit_child_node->GetDelegate()->GetData().id);
+  }
+}
+
 }  // namespace content

content/browser/renderer_host/render_widget_host_view_aura.cc

@@ -825,6 +825,7 @@ void RenderWidgetHostViewAura::OnLegacyWindowDestroyed() {
   legacy_render_widget_host_HWND_ = nullptr;
   legacy_window_destroyed_ = true;
 }
+#endif
 
 gfx::NativeViewAccessible
 RenderWidgetHostViewAura::GetParentNativeViewAccessible() {
@@ -842,7 +843,6 @@ RenderWidgetHostViewAura::GetParentNativeViewAccessible() {
 
   return nullptr;
 }
-#endif
 
 void RenderWidgetHostViewAura::ResetFallbackToFirstNavigationSurface() {
   if (delegated_frame_host_)

content/browser/renderer_host/render_widget_host_view_aura.h

@@ -303,9 +303,9 @@ class CONTENT_EXPORT RenderWidgetHostViewAura
 
   // Notification that the LegacyRenderWidgetHostHWND was destroyed.
   void OnLegacyWindowDestroyed();
+#endif
 
   gfx::NativeViewAccessible GetParentNativeViewAccessible();
-#endif
 
   // Method to indicate if this instance is shutting down or closing.
   // TODO(shrikant): Discuss around to see if it makes sense to add this method

ui/accessibility/platform/ax_platform_node_auralinux.cc

@@ -4176,7 +4176,30 @@ gfx::NativeViewAccessible
 AXPlatformNodeAuraLinux::HitTestSync(gint x, gint y, AtkCoordType coord_type) {
   gfx::Point scroll_to(x, y);
   scroll_to = ConvertPointToScreenCoordinates(scroll_to, coord_type);
-  return delegate_->HitTestSync(scroll_to.x(), scroll_to.y());
+
+  AXPlatformNode* current_result = this;
+  while (true) {
+    gfx::NativeViewAccessible hit_child =
+        current_result->GetDelegate()->HitTestSync(scroll_to.x(),
+                                                   scroll_to.y());
+    if (!hit_child)
+      return nullptr;
+    AXPlatformNode* hit_child_node =
+        AXPlatformNode::FromNativeViewAccessible(hit_child);
+    if (!hit_child_node || !hit_child_node->IsDescendantOf(current_result))
+      break;
+
+    // If we get the same node, we're done.
+    if (hit_child_node == current_result)
+      break;
+
+    // Continue to check recursively. That's because HitTestSync may have
+    // returned the best result within a particular accessibility tree,
+    // but we might need to recurse further in a tree of a different type
+    // (for example, from Views to Web).
+    current_result = hit_child_node;
+  }
+  return current_result->GetNativeViewAccessible();
 }
 
 bool AXPlatformNodeAuraLinux::GrabFocus() {