Low-hanging optimization for ITextRangeProvider::GetChildren

|LowestCommonAnchor| is always cheaper than |LowestCommonAncestor|
when the ancestor position data is not needed.

AXPlatformNodeTextRangeProviderWin::GetChildren does not use the
position information, all information is available on the AXNode
from calling |LowestCommonAnchor|.

Bug: 928948
Change-Id: I48075202dca0172bfd6deea9188d3d636f996ac2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1815224
Commit-Queue: Adam Ettenberger <adettenb@microsoft.com>
Reviewed-by: Kevin Babbitt <kbabbitt@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#699033}

ui/accessibility/platform/ax_platform_node_textrangeprovider_win.cc

@@ -765,13 +765,10 @@ STDMETHODIMP AXPlatformNodeTextRangeProviderWin::GetChildren(
 
   std::vector<gfx::NativeViewAccessible> descendants;
 
-  AXPositionInstance common_ancestor =
-      start_->LowestCommonAncestor(*end_.get());
-
-  AXPlatformNodeDelegate* delegate =
-      GetDelegate(common_ancestor.get())
-          ->GetFromNodeID(common_ancestor->anchor_id())
-          ->GetDelegate();
+  const AXNode* common_anchor = start_->LowestCommonAnchor(*end_);
+  const AXTreeID tree_id = common_anchor->tree()->GetAXTreeID();
+  const AXNode::AXID node_id = common_anchor->id();
+  AXPlatformNodeDelegate* delegate = GetDelegate(tree_id, node_id);
   DCHECK(delegate);
   while (ui::IsIgnored(delegate->GetData())) {
     auto* node = static_cast<AXPlatformNodeWin*>(