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

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 4c48b6f07ee54108b33b997b6bc7d7470f378605..1bd0a7a52bdf7be175d185036e04e6bca6516318 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -3030,6 +3030,10 @@ bool Document::shouldMergeWithLegacyDescription(ViewportDescription::Type origin
 
 void Document::setViewportDescription(const ViewportDescription& viewportDescription)
 {
+    // The UA-defined min-width is used by the processing of legacy meta tags.
+    if (!viewportDescription.isSpecifiedByAuthor())
+        m_viewportDefaultMinWidth = viewportDescription.minWidth;
+
     if (viewportDescription.isLegacyViewportType()) {
         if (settings() && !settings()->viewportMetaEnabled())
             return;