Convert usage of banned std::to_string() to base::IntToString().

athena/wm/window_list_provider_impl_unittest.cc

Index: athena/wm/window_list_provider_impl_unittest.cc
diff --git a/athena/wm/window_list_provider_impl_unittest.cc b/athena/wm/window_list_provider_impl_unittest.cc
index 402f20f0ec2d6ff3c4b76992f233a86e0be47769..b8fa76497b1903745bf48c4da5efae0d5fa7fb56 100644
--- a/athena/wm/window_list_provider_impl_unittest.cc
+++ b/athena/wm/window_list_provider_impl_unittest.cc
@@ -11,6 +11,7 @@
 #include "athena/test/base/test_windows.h"
 #include "athena/wm/public/window_list_provider_observer.h"
 #include "athena/wm/public/window_manager.h"
+#include "base/strings/string_number_conversions.h"
 #include "ui/aura/client/window_tree_client.h"
 #include "ui/aura/test/test_window_delegate.h"
 #include "ui/aura/window.h"
@@ -50,7 +51,7 @@ std::string GetWindowOrder(const aura::Window::Windows& original,
     for (size_t i = 0; i < original.size(); i++) {
       if ((*it) == original[i]) {
         output += (output.size() ? " " : std::string()) +
-                  std::to_string(i + 1);
+                  base::IntToString(i + 1);
         break;
       }
     }