Translate viewport related meta tags into @viewport descriptors as suggested by the CSS Device Adap…

Source/core/css/CSSPrimitiveValue.cpp

Index: Source/core/css/CSSPrimitiveValue.cpp
diff --git a/Source/core/css/CSSPrimitiveValue.cpp b/Source/core/css/CSSPrimitiveValue.cpp
index 8281371d994565f9849f3bc7fc1cec9341fe7965..3104e28f954abb07704707b1f5d440181fcb16ee 100644
--- a/Source/core/css/CSSPrimitiveValue.cpp
+++ b/Source/core/css/CSSPrimitiveValue.cpp
@@ -311,6 +311,10 @@ CSSPrimitiveValue::CSSPrimitiveValue(const Length& length)
             m_primitiveUnitType = CSS_VALUE_ID;
             m_value.valueID = CSSValueWebkitFitContent;
             break;
+        case ExtendToZoom:
+            m_primitiveUnitType = CSS_VALUE_ID;
+            m_value.valueID = CSSValueExtendToZoom;
+            break;
         case Percent:
             m_primitiveUnitType = CSS_PERCENTAGE;
             ASSERT(std::isfinite(length.percent()));