MAGETWO-39503: "Same as shipping" check box checked by default

Author: Olexii Korshenko

app/code/Magento/Checkout/view/frontend/web/js/action/select-shipping-address.js

@@ -14,6 +14,10 @@ define(
         });
         return function(shippingAddress) {
             quote.shippingAddress(shippingAddress);
+            //set billing address same as shipping by default
+            if (shippingAddress.canUseForBilling()) {
+                quote.billingAddress(shippingAddress);
+            }
         };
     }
 );