function Document(docDefinition, tableLayouts, fonts, vfs) {
	this.docDefinition = docDefinition;
	this.tableLayouts = tableLayouts || null;
	this.fonts = fonts || defaultClientFonts;
	this.vfs = vfs;
}
Measures all nodes and sets min/max-width properties required for the second
layout-pass.
@param  {Object} docStructure document-definition-object
@return {Object}              document-measurement-object