This file uses comments a bit excessively. We should refactor the logic so that the comments are replaced by subfunctions. 

For instance, a code snippet such as:

  // |action_buttons_row_| contains inline action buttons.
  action_buttons_row_ = new views::View();
  action_buttons_row_->SetLayoutManager(std::make_unique<views::BoxLayout>(
      views::BoxLayout::kHorizontal, kActionsRowPadding,
      kActionsRowHorizontalSpacing));
  action_buttons_row_->SetBackground(
      views::CreateSolidBackground(kActionsRowBackgroundColor));
  action_buttons_row_->SetVisible(false);
  actions_row_->AddChildView(action_buttons_row_);

should be factored out into a function where the name of the function fulfills the role currently served by the comment.