Bug 1397577 - Avoid using GetChildAt() in HTMLEditor::GetSelectedOrParentTableElement(); r=smaug

dom/base/Selection.cpp

@@ -923,6 +923,19 @@ Selection::FocusOffset()
   return mAnchorFocusRange->StartOffset();
 }
 
+nsIContent*
+Selection::GetChildAtAnchorOffset()
+{
+  if (!mAnchorFocusRange)
+    return nullptr;
+
+  if (GetDirection() == eDirNext) {
+    return mAnchorFocusRange->GetChildAtStartOffset();
+  }
+
+  return mAnchorFocusRange->GetChildAtEndOffset();
+}
+
 static nsresult
 CompareToRangeStart(nsINode* aCompareNode, int32_t aCompareOffset,
                     nsRange* aRange, int32_t* aCmp)

dom/base/Selection.h

@@ -171,6 +171,8 @@ public:
   nsINode*     GetFocusNode();
   uint32_t     FocusOffset();
 
+  nsIContent*  GetChildAtAnchorOffset();
+
   /*
    * IsCollapsed -- is the whole selection just one point, or unset?
    */

editor/libeditor/HTMLTableEditor.cpp

@@ -3201,8 +3201,7 @@ HTMLEditor::GetSelectedOrParentTableElement(nsAString& aTagName,
 
     // Get child of anchor node, if exists
     if (anchorNode->HasChildNodes()) {
-      int32_t anchorOffset = selection->AnchorOffset();
-      nsINode* selectedNode = anchorNode->GetChildAt(anchorOffset);
+      nsINode* selectedNode = selection->GetChildAtAnchorOffset();
       if (!selectedNode) {
         selectedNode = anchorNode;
         // If anchor doesn't have a child, we can't be selecting a table element,