Output warning when the container window doesn't exist unexpectedly

ui/keyboard/keyboard_controller.cc

 // Copyright (c) 2013 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 "ui/keyboard/keyboard_controller.h"
 
 #include <set>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 388 matching lines @@
   input_method_ = NULL;
 }
 
 void KeyboardController::OnShowImeIfNeeded() {
   // Calling |ShowKeyboardInternal| may move the keyboard to another display.
   if (IsKeyboardEnabled() && !keyboard_locked())
     ShowKeyboardInternal(display::kInvalidDisplayId);
 }
 
 void KeyboardController::ShowKeyboardInternal(int64_t display_id) {
-  if (!container_.get())
+  DCHECK(container_.get());
+  if (!container_.get()) {
+    LOG(WARNING) << "container_ was not initialized unexpectedly.";

[bshe, 2017/04/10 13:38:37]

If you have a DCHECK, you shouldn't need to handle its failure:
https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md...

If container_.get() can't be null, perhaps remove the if check?

[oka, 2017/04/13 09:07:57]

Done. I added DCHECK only and commened the rationale why the window should exist
there.

     return;
+  }
 
   if (container_->children().empty()) {
     keyboard::MarkKeyboardLoadStarted();
     aura::Window* keyboard = ui_->GetKeyboardWindow();
     keyboard->Show();
     container_->AddChild(keyboard);
     keyboard->set_owned_by_parent(false);
   }
 
   ui_->ReloadKeyboardIfNeeded();
@@ skipping 97 matching lines @@
     int keyboard_height = GetContainerWindow()->bounds().height();
     const gfx::Rect& root_bounds = container_->GetRootWindow()->bounds();
     gfx::Rect new_bounds = root_bounds;
     new_bounds.set_y(root_bounds.height() - keyboard_height);
     new_bounds.set_height(keyboard_height);
     GetContainerWindow()->SetBounds(new_bounds);
   }
 }
 
 }  // namespace keyboard