Fix assert on Mandoline shutdown.

mandoline/tab/frame.cc

 // Copyright 2015 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 "mandoline/tab/frame.h"
 
 #include <algorithm>
 
 #include "base/stl_util.h"
 #include "components/view_manager/public/cpp/view.h"
@@ skipping 25 matching lines @@
     *services = GetProxy(&services_).Pass();
 
   if (exposed_services) {
     mojo::ServiceProviderPtr exposed_services_ptr;
     exposed_services_.Bind(GetProxy(&exposed_services_ptr));
     *exposed_services = exposed_services_ptr.Pass();
   }
 }
 
 Frame::~Frame() {
-  view_->RemoveObserver(this);
+  if (view_)
+    view_->RemoveObserver(this);
   STLDeleteElements(&children_);
   if (parent_)
     parent_->Remove(this);
-  view_->ClearLocalProperty(kFrame);
+  if (view_)
+    view_->ClearLocalProperty(kFrame);
   if (view_ownership_ == ViewOwnership::OWNS_VIEW)
     view_->Destroy();
 }
 
 // static
 Frame* Frame::FindFirstFrameAncestor(View* view) {
   while (view && !view->GetLocalProperty(kFrame))
     view = view->parent();
   return view ? view->GetLocalProperty(kFrame) : nullptr;
 }
@@ skipping 10 matching lines @@
   DCHECK_EQ(node->parent_, this);
   auto iter = std::find(children_.begin(), children_.end(), node);
   DCHECK(iter != children_.end());
   node->parent_ = nullptr;
   children_.erase(iter);
 }
 
 void Frame::OnViewDestroying(mojo::View* view) {
   if (parent_)
     parent_->Remove(this);
-  // Assume the view associated with the root is never deleted out from under
-  // us.
-  // TODO(sky): this is likely bogus. Change browser to create a child for
-  // each FrameTree.
-  DCHECK_NE(this, tree_->root());
 
   // Reset |view_ownership_| so we don't attempt to delete |view_| in the
   // destructor.
   view_ownership_ = ViewOwnership::DOESNT_OWN_VIEW;
+
+  // Assume the view associated with the root is never deleted out from under
+  // us.
+  // TODO(sky): Change browser to create a child for each FrameTree.
+  if (tree_->root() == this) {
+    view_->RemoveObserver(this);
+    view_ = nullptr;
+    return;
+  }
+
   delete this;
 }
 
 }  // namespace mandoline