Network config: nameservers: clear empty

Don't display empty nameservers when switching from custom -> automatic.

Bug: 801087
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ia4111f044368411773a0cbfb94cf129231f72845
Reviewed-on: https://chromium-review.googlesource.com/896267Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533789}

ui/webui/resources/cr_components/chromeos/network/network_nameservers.js

@@ -99,6 +99,7 @@ Polymer({
       }
     } else {
       type = 'automatic';
+      nameservers = this.clearEmptyNameServers_(nameservers);
     }
     this.setNameservers_(type, nameservers, false /* send */);
   },
@@ -213,13 +214,14 @@ Polymer({
         field: 'NameServers',
         value: this.GOOGLE_NAMESERVERS,
       });
-    } else {
-      // automatic
+    } else {  // type == automatic
       // If not connected, properties will clear. Otherwise they may or may not
       // change so leave them as-is.
       if (this.networkProperties.ConnectionState !=
           CrOnc.ConnectionState.CONNECTED) {
         this.nameservers_ = [];
+      } else {
+        this.nameservers_ = this.clearEmptyNameServers_(this.nameservers_);
       }
       this.fire('nameservers-change', {
         field: 'NameServersConfigType',
@@ -227,4 +229,13 @@ Polymer({
       });
     }
   },
+
+  /**
+   * @param {!Array<string>} nameservers
+   * @return {!Array<string>}
+   * @private
+   */
+  clearEmptyNameServers_: function(nameservers) {
+    return nameservers.filter((nameserver) => !!nameserver);
+  },
 });