Convert dom_distiller::WebContentsMainFrameObserver to use the new navigation callbacks.

content/test/web_contents_observer_sanity_checker.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/test/web_contents_observer_sanity_checker.h"
 
 #include "base/strings/stringprintf.h"
 #include "build/build_config.h"
 #include "content/browser/frame_host/render_frame_host_impl.h"
 #include "content/common/frame_messages.h"
@@ skipping 109 matching lines @@
       CHECK(false)
           << "RenderFrameHostChanged called with old host that did not exist:"
           << Format(old_host);
     }
     CHECK(!HasAnyChildren(old_host))
         << "All children should be detached before a parent is detached.";
   }
 
   EnsureStableParentValue(new_host);
   if (new_host->GetParent()) {
-    AssertRenderFrameExists(new_host->GetParent());
+    //
+    //AssertRenderFrameExists(new_host->GetParent());

[nyquist, 2017/02/01 07:10:04]

It looks from the comments in the test code that the change to this file should
be scrapped now?

[jam, 2017/02/01 15:31:04]

Ooops, thanks fixed.

     CHECK(current_hosts_.count(GetRoutingPair(new_host->GetParent())))
         << "Parent of frame being committed must be current.";
   }
 
   GlobalRoutingID routing_pair = GetRoutingPair(new_host);
   bool host_exists = !current_hosts_.insert(routing_pair).second;
   if (host_exists) {
     CHECK(false)
         << "RenderFrameHostChanged called more than once for routing pair:"
         << Format(new_host);
@@ skipping 265 matching lines @@
       if (live_routes_.count(entry.first))
         return true;
       if (current_hosts_.count(entry.first))
         return true;
     }
   }
   return false;
 }
 
 }  // namespace content