MAGETWO-83000: [Backport 2.1-develop] #11697 Theme: Added html node t…

…o page xml root, cause validation error #11861

 - Merge Pull Request #11861 from adrian-martinez-interactiv4/magento2:FR21#THEME-HTML-NODE-PAGE-XML-ROOT
 - Merged commits:
   1. 2370f14

lib/internal/Magento/Framework/View/Layout/etc/layout_merged.xsd

@@ -9,6 +9,7 @@
     <xs:include schemaLocation="urn:magento:framework:View/Layout/etc/elements.xsd"/>
     <xs:include schemaLocation="urn:magento:framework:View/Layout/etc/head.xsd"/>
     <xs:include schemaLocation="urn:magento:framework:View/Layout/etc/body.xsd"/>
+    <xs:include schemaLocation="urn:magento:framework:View/Layout/etc/html.xsd"/>
 
     <xs:element name="layout">
         <xs:annotation>
@@ -45,6 +46,7 @@
             <xs:element ref="referenceBlock" minOccurs="0" maxOccurs="unbounded"/>
             <xs:element name="body" type="bodyType" minOccurs="0" maxOccurs="unbounded"/>
             <xs:element name="head" type="headType" minOccurs="0" maxOccurs="unbounded"/>
+            <xs:element name="html" type="htmlType" minOccurs="0" maxOccurs="unbounded"/>
         </xs:choice>
     </xs:complexType>