Linux Aura: get tooltip background color from theme

ui/native_theme/native_theme.h

 // Copyright (c) 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.
 
 #ifndef UI_NATIVE_THEME_NATIVE_THEME_H_
 #define UI_NATIVE_THEME_NATIVE_THEME_H_
 
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/native_widget_types.h"
 #include "ui/native_theme/native_theme_export.h"
@@ skipping 247 matching lines @@
     kColorId_LabelEnabledColor,
     kColorId_LabelDisabledColor,
     kColorId_LabelBackgroundColor,
     // Textfield
     kColorId_TextfieldDefaultColor,
     kColorId_TextfieldDefaultBackground,
     kColorId_TextfieldReadOnlyColor,
     kColorId_TextfieldReadOnlyBackground,
     kColorId_TextfieldSelectionColor,
     kColorId_TextfieldSelectionBackgroundFocused,
+    // Tooltip
+    kColorId_TooltipBackground,
     // Tree
     kColorId_TreeBackground,
     kColorId_TreeText,
     kColorId_TreeSelectedText,
     kColorId_TreeSelectedTextUnfocused,
     kColorId_TreeSelectionBackgroundFocused,
     kColorId_TreeSelectionBackgroundUnfocused,
     kColorId_TreeArrow,
     // Table
     kColorId_TableBackground,
@@ skipping 39 matching lines @@
   unsigned int thumb_inactive_color_;
   unsigned int thumb_active_color_;
   unsigned int track_color_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeTheme);
 };
 
 }  // namespace ui
 
 #endif  // UI_NATIVE_THEME_NATIVE_THEME_H_