Do not create proxy hosts in the subtree of navigating frame.

content/browser/frame_host/frame_tree_browsertest.cc

Index: content/browser/frame_host/frame_tree_browsertest.cc
diff --git a/content/browser/frame_host/frame_tree_browsertest.cc b/content/browser/frame_host/frame_tree_browsertest.cc
index 36b2cd4c8b0ae6d294629e78c893071b679f806e..4fe00acc816113478dc6b4b7f6b37d9c5f7541b1 100644
--- a/content/browser/frame_host/frame_tree_browsertest.cc
+++ b/content/browser/frame_host/frame_tree_browsertest.cc
@@ -247,7 +247,7 @@ IN_PROC_BROWSER_TEST_F(CrossProcessFrameTreeBrowserTest,
   NavigateFrameToURL(root->child_at(0), cross_site_url);
 
   // Ensure that we have created a new process for the subframe.
-  ASSERT_EQ(1U, root->child_count());
+  ASSERT_EQ(2U, root->child_count());
   FrameTreeNode* child = root->child_at(0);
   SiteInstance* child_instance = child->current_frame_host()->GetSiteInstance();
   RenderViewHost* rvh = child->current_frame_host()->render_view_host();