Make <meter> transparent if -webkit-appearance:none or background CSS property is specified.

third_party/WebKit/Source/core/layout/LayoutTheme.cpp

 /**
  * This file is part of the theme implementation for form controls in WebCore.
  *
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 372 matching lines @@
     return appearance != CheckboxPart && appearance != RadioPart;
 }
 
 bool LayoutTheme::isControlStyled(const ComputedStyle& style) const
 {
     switch (style.appearance()) {
     case PushButtonPart:
     case SquareButtonPart:
     case ButtonPart:
     case ProgressBarPart:
-    case MeterPart:
     case RelevancyLevelIndicatorPart:
     case ContinuousCapacityLevelIndicatorPart:
     case DiscreteCapacityLevelIndicatorPart:
     case RatingLevelIndicatorPart:
         return style.hasAuthorBackground() || style.hasAuthorBorder();
 
+    case MeterPart:
+        return style.hasAuthorBackground();
+
     case MenulistPart:
     case SearchFieldPart:
     case TextAreaPart:
     case TextFieldPart:
         return style.hasAuthorBackground() || style.hasAuthorBorder() || style.boxShadow();
 
     case SliderHorizontalPart:
     case SliderVerticalPart:
         return style.boxShadow();
 
@@ skipping 527 matching lines @@
 
     // padding - not honored by WinIE, needs to be removed.
     style.resetPadding();
 
     // border - honored by WinIE, but looks terrible (just paints in the control box and turns off the Windows XP theme)
     // for now, we will not honor it.
     style.resetBorder();
 }
 
 } // namespace blink