Use correct position when setting pos_in_set for tabs.

ui/accessibility/ax_node_data.cc

Index: ui/accessibility/ax_node_data.cc
diff --git a/ui/accessibility/ax_node_data.cc b/ui/accessibility/ax_node_data.cc
index 82e35d6fab3a4ddc97dc39ce03e8611f63ad6664..0a339bdcec3edcb4dab941f7d6152aa6086359b7 100644
--- a/ui/accessibility/ax_node_data.cc
+++ b/ui/accessibility/ax_node_data.cc
@@ -369,6 +369,21 @@ void AXNodeData::AddIntAttribute(
   int_attributes.push_back(std::make_pair(attribute, value));
 }
 
+void AXNodeData::AddValidatedIntAttribute(AXValidatedIntAttribute attribute,
+                                          int value) {
+  switch (attribute) {
+    case ui::AX_ATTR_INDEX_IN_SET:
+      if (value < 0) {
+        NOTREACHED();
+        return;
+      }
+      AddIntAttribute(ui::AX_ATTR_POS_IN_SET, value + 1);
+      break;
+    default:
+      NOTREACHED();
+  }
+}
+
 void AXNodeData::AddFloatAttribute(
     AXFloatAttribute attribute, float value) {
   float_attributes.push_back(std::make_pair(attribute, value));