Bug 1658702 - part 15: Implement shortcut case of...

Bug 1658702 - part 15: Implement shortcut case of `AutoDeleteRangesHandler::HandleDeleteNonCollapsedRanges()` r=m_kato

This patch corresponds to:
* https://searchfox.org/mozilla-central/rev/0c97a6410ff018c22e65a0cbe4e5f2ca4581b22e/editor/libeditor/HTMLEditSubActionHandler.cpp#4500-4527

Depends on D90211

Differential Revision: https://phabricator.services.mozilla.com/D90212

editor/libeditor/HTMLEditSubActionHandler.cpp

@@ -4956,6 +4956,23 @@ HTMLEditor::AutoDeleteRangesHandler::ComputeRangesToDeleteNonCollapsedRanges(
     }
   }
+  if (aRangesToDelete.FirstRangeRef()->GetStartContainer() ==
+      aRangesToDelete.FirstRangeRef()->GetEndContainer()) {
+    if (!aRangesToDelete.FirstRangeRef()->Collapsed()) {
+      nsresult rv = ComputeRangesToDeleteRangesWithTransaction(
+          aHTMLEditor, aDirectionAndAmount, aStripWrappers, aRangesToDelete);
+      NS_WARNING_ASSERTION(
+          NS_SUCCEEDED(rv),
+          "AutoDeleteRangesHandler::ComputeRangesToDeleteRangesWithTransaction("
+          ") failed");
+      return rv;
+    }
+    // `DeleteUnnecessaryNodesAndCollapseSelection()` may delete parent
+    // elements, but it does not affect computing target ranges.  Therefore,
+    // we don't need to touch aRangesToDelete in this case.
+    return NS_OK;
+  }
+
   Element* startCiteNode = aHTMLEditor.GetMostAncestorMailCiteElement(
       *aRangesToDelete.FirstRangeRef()->GetStartContainer());
   Element* endCiteNode = aHTMLEditor.GetMostAncestorMailCiteElement(