Decouple font unit conversion in computeLengthDouble from RenderStyle.

Source/core/css/resolver/ViewportStyleResolver.cpp

Index: Source/core/css/resolver/ViewportStyleResolver.cpp
diff --git a/Source/core/css/resolver/ViewportStyleResolver.cpp b/Source/core/css/resolver/ViewportStyleResolver.cpp
index dba44849fda6c31920b9f4b1becb7e06c1d2f090..c39db69b018804c83c240b954e87c94299f014d6 100644
--- a/Source/core/css/resolver/ViewportStyleResolver.cpp
+++ b/Source/core/css/resolver/ViewportStyleResolver.cpp
@@ -189,7 +189,9 @@ Length ViewportStyleResolver::viewportLengthValue(CSSPropertyID id) const
     float width = view ? view->width() : 0;
     float height = view ? view->height() : 0;
 
-    Length result = primitiveValue->convertToLength<AnyConversion>(CSSToLengthConversionData(documentStyle, documentStyle, width, height, 1.0f));
+    CSSToLengthFontSizes fontSizes(documentStyle, documentStyle);
+    CSSToLengthViewportSize viewportSize(width, height);
+    Length result = primitiveValue->convertToLength<AnyConversion>(CSSToLengthConversionData(documentStyle, fontSizes, viewportSize, 1.0f));
     if (documentStyle->hasViewportUnits())
         m_document->setHasViewportUnits();
     documentStyle->setHasViewportUnits(documentStyleHasViewportUnits);