Adds some DCHECKs to help isolate flake

services/ui/ws/window_tree.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 "services/ui/ws/window_tree.h"
 
 #include <stddef.h>
 
 #include <utility>
 
@@ skipping 97 matching lines @@
   ClientWindowId focused_window_id;
   if (focused_window)
     IsWindowKnown(focused_window, &focused_window_id);
 
   const bool drawn = root->parent() && root->parent()->IsDrawn();
   client()->OnEmbed(id_, WindowToWindowData(to_send.front()), std::move(tree),
                     display_id, focused_window_id.id, drawn);
 }
 
 void WindowTree::ConfigureWindowManager() {
+  // ConfigureWindowManager() should be called early on, before anything
+  // else. |waiting_for_top_level_window_info_| must be null as if
+  // |waiting_for_top_level_window_info_| is non-null it means we're about to
+  // create an associated interface, which doesn't work with pause/resume.
+  // TODO(sky): DCHECK temporary until 626869 is sorted out.
+  DCHECK(!waiting_for_top_level_window_info_);
   DCHECK(!window_manager_internal_);
   window_manager_internal_ = binding_->GetWindowManager();
   window_manager_internal_->OnConnect(id_);
   window_manager_state_.reset(new WindowManagerState(this));
 }
 
 const ServerWindow* WindowTree::GetWindow(const WindowId& id) const {
   if (id_ == id.client_id) {
     auto iter = created_window_map_.find(id);
     return iter == created_window_map_.end() ? nullptr : iter->second;
@@ skipping 876 matching lines @@
   }
   client()->OnChangeCompleted(
       change_id, NewWindow(ClientWindowId(transport_window_id), properties));
 }
 
 void WindowTree::NewTopLevelWindow(
     uint32_t change_id,
     Id transport_window_id,
     mojo::Map<mojo::String, mojo::Array<uint8_t>> transport_properties) {
   DCHECK(!waiting_for_top_level_window_info_);
+  // TODO(sky): rather than DCHECK, have this kill connection.
+  DCHECK(!window_manager_internal_);  // Not valid for the windowmanager.
   const ClientWindowId client_window_id(transport_window_id);
   // TODO(sky): need a way for client to provide context to figure out display.
   Display* display = display_manager()->displays().empty()
                          ? nullptr
                          : *(display_manager()->displays().begin());
   // TODO(sky): move checks to accesspolicy.
   WindowManagerDisplayRoot* display_root =
       display && user_id_ != InvalidUserId()
           ? display->GetWindowManagerDisplayRootForUser(user_id_)
           : nullptr;
@@ skipping 637 matching lines @@
 }
 
 bool WindowTree::IsWindowRootOfAnotherTreeForAccessPolicy(
     const ServerWindow* window) const {
   WindowTree* tree = window_server_->GetTreeWithRoot(window);
   return tree && tree != this;
 }
 
 }  // namespace ws
 }  // namespace ui