Read the default min-width value from the UA style sheets

Source/core/dom/ViewportDescription.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2012-2013 Intel Corporation. All rights reserved.
  *
@@ skipping 52 matching lines @@
     if (length.type() == DeviceWidth)
         return initialViewportSize.width();
 
     if (length.type() == DeviceHeight)
         return initialViewportSize.height();
 
     ASSERT_NOT_REACHED();
     return ViewportDescription::ValueAuto;
 }
 
-PageScaleConstraints ViewportDescription::resolve(const FloatSize& initialViewportSize) const
+PageScaleConstraints ViewportDescription::resolve(const FloatSize& initialViewportSize, Length legacyFallbackWidth) const
 {
     float resultWidth = ValueAuto;
-    float resultMaxWidth = resolveViewportLength(maxWidth, initialViewportSize, Horizontal);
-    float resultMinWidth = resolveViewportLength(minWidth, initialViewportSize, Horizontal);
+
+    Length copyMaxWidth = maxWidth;
+    Length copyMinWidth = minWidth;
+    // In case the width (used for min- and max-width) is undefined.
+    if (isLegacyViewportType() && maxWidth.isAuto()) {
+        // The width viewport META property is translated into 'width' descriptors, setting
+        // the 'min' value to 'extend-to-zoom' and the 'max' value to the intended length.
+        // In case the UA-defines a min-width, use that as length.
+        if (zoom == ViewportDescription::ValueAuto) {
+            copyMinWidth = Length(ExtendToZoom);
+            copyMaxWidth = legacyFallbackWidth;
+        } else if (maxHeight.isAuto()) {
+            copyMinWidth = Length(ExtendToZoom);
+            copyMaxWidth = Length(ExtendToZoom);
+        }
+    }
+
+    float resultMaxWidth = resolveViewportLength(copyMaxWidth, initialViewportSize, Horizontal);
+    float resultMinWidth = resolveViewportLength(copyMinWidth, initialViewportSize, Horizontal);
+
     float resultHeight = ValueAuto;
     float resultMaxHeight = resolveViewportLength(maxHeight, initialViewportSize, Vertical);
     float resultMinHeight = resolveViewportLength(minHeight, initialViewportSize, Vertical);
 
     float resultZoom = zoom;
     float resultMinZoom = minZoom;
     float resultMaxZoom = maxZoom;
     float resultUserZoom = userZoom;
 
     // 1. Resolve min-zoom and max-zoom values.
@@ skipping 82 matching lines @@
     PageScaleConstraints result;
     result.minimumScale = resultMinZoom;
     result.maximumScale = resultMaxZoom;
     result.initialScale = resultZoom;
     result.layoutSize.setWidth(resultWidth);
     result.layoutSize.setHeight(resultHeight);
     return result;
 }
 
 } // namespace WebCore