Fixed test by changing the way a subframe was added.

content/browser/frame_host/navigator_impl_unittest.cc

Index: content/browser/frame_host/navigator_impl_unittest.cc
diff --git a/content/browser/frame_host/navigator_impl_unittest.cc b/content/browser/frame_host/navigator_impl_unittest.cc
index 6f692afdaadaa93e84debf83598870be7123318f..2de47f8cf685e8a83c1c3ff3d447f77c4152883c 100644
--- a/content/browser/frame_host/navigator_impl_unittest.cc
+++ b/content/browser/frame_host/navigator_impl_unittest.cc
@@ -133,10 +133,7 @@ TEST_F(NavigatorTestWithBrowserSideNavigation, BeginNavigation) {
 
   // Add a subframe.
   FrameTreeNode* root_node = contents()->GetFrameTree()->root();
-  TestRenderFrameHost* subframe_rfh =
-      static_cast<TestRenderFrameHost*>(contents()->GetFrameTree()->AddFrame(
-          root_node, root_node->current_frame_host()->GetProcess()->GetID(), 14,
-          "Child"));
+  TestRenderFrameHost* subframe_rfh = main_test_rfh()->AppendChild("Child");
   ASSERT_TRUE(subframe_rfh);
 
   FrameTreeNode* subframe_node = subframe_rfh->frame_tree_node();