[Ash] Disallow calling HoverHighlightView::SetSubText() with an empty string

ash/system/tray/hover_highlight_view.cc

 // Copyright 2012 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 "ash/system/tray/hover_highlight_view.h"
 
 #include "ash/resources/vector_icons/vector_icons.h"
 #include "ash/system/tray/tray_constants.h"
 #include "ash/system/tray/tray_popup_utils.h"
 #include "ash/system/tray/tri_view.h"
@@ skipping 38 matching lines @@
 
 void HoverHighlightView::SetRightViewVisible(bool visible) {
   if (!right_view_)
     return;
 
   right_view_->SetVisible(visible);
   Layout();
 }
 
 void HoverHighlightView::SetSubText(const base::string16& sub_text) {
+  if (sub_text.empty())

[mohsen, 2017/04/27 19:39:37]

We should either disallow empty string altogether (by DCHECKing) or at least
clear the |sub_text_label_|'s text if it already exists (if we don't want to
remove the label entirely). WDYT?

[tdanderson, 2017/04/27 20:52:16]

Done.

+    return;
+
   DCHECK(text_label_);
 
   if (!sub_text_label_) {
     sub_text_label_ = TrayPopupUtils::CreateDefaultLabel();
     tri_view_->AddView(TriView::Container::CENTER, sub_text_label_);
   }
+
   TrayPopupItemStyle sub_style(TrayPopupItemStyle::FontStyle::CAPTION);
   sub_style.set_color_style(TrayPopupItemStyle::ColorStyle::INACTIVE);
   sub_style.SetupLabel(sub_text_label_);
   sub_text_label_->SetText(sub_text);
 }
 
 void HoverHighlightView::AddIconAndLabel(const gfx::ImageSkia& image,
                                          const base::string16& text) {
   DoAddIconAndLabel(image, text,
                     TrayPopupItemStyle::FontStyle::DETAILED_VIEW_LABEL);
@@ skipping 123 matching lines @@
   if (right_view_)
     right_view_->SetEnabled(enabled());
 }
 
 void HoverHighlightView::OnFocus() {
   ScrollRectToVisible(gfx::Rect(gfx::Point(), size()));
   ActionableView::OnFocus();
 }
 
 }  // namespace ash