add ancestry path support

Author: Abhishek Bindra

lib/core/utils/get-ancestry.js

@@ -13,8 +13,29 @@ function generateAncestry(node) {
     nodeName !== 'body' &&
     parent.children.length > 1
   ) {
-    const index = Array.prototype.indexOf.call(parent.children, node) + 1;
-    nthChild = `:nth-child(${index})`;
+    let index = 0;
+    if (parent.nodeName === 'BODY') {
+      let count = 0;
+      // Single pass over siblings: count valid children & locate node position.
+      for (
+        let sib = parent.firstElementChild;
+        sib;
+        sib = sib.nextElementSibling
+      ) {
+        if (sib.hasAttribute('data-percy-injected')) {
+          continue;
+        }
+        count++;
+        if (sib === node) {
+          index = count;
+          break;
+        }
+      }
+      nthChild = count > 1 ? `:nth-child(${index})` : '';
+    } else {
+      index = Array.prototype.indexOf.call(parent.children, node) + 1;
+      nthChild = `:nth-child(${index})`;
+    }
   }
 
   return generateAncestry(parent) + ' > ' + nodeName + nthChild;