Reduce boilerplace when accessing frame_tree and NavigationController.

Adds a frame_tree() accessor to RenderFrameHostImpl.

Adds an accessor for NavigationControllerImpl to FrameTree.

Using both of these, remove a lot of chained accesses in code.

Change-Id: Ic195217e249eb41744a0d7fd8f77340ab708ce07
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2212185
Commit-Queue: Fergal Daly <[email protected]>
Reviewed-by: Nasko Oskov <[email protected]>
Cr-Commit-Position: refs/heads/master@{#774034}
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 28734c1..b89bdda 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -1822,8 +1822,7 @@
   DCHECK(!inner_web_contents_impl->node_.outer_web_contents());
   auto* render_frame_host_impl =
       static_cast<RenderFrameHostImpl*>(render_frame_host);
-  DCHECK_EQ(&frame_tree_,
-            render_frame_host_impl->frame_tree_node()->frame_tree());
+  DCHECK_EQ(&frame_tree_, render_frame_host_impl->frame_tree());
 
   RenderFrameHostManager* inner_render_manager =
       inner_web_contents_impl->GetRenderManager();