GML parser.

This adds a parser (read/write) for GML v2 and v3. GML v3 is limited to the
simple features profile of GML 3.1.1, just like OpenLayers 2 was. This will
be the basis for the WFS parser, but it only makes sense to continue this work
once feature modification (insert, update, delete) is in place in ol3. So the
WFS parser will be another pull request.

src/ol/parser/xml.js

@@ -1,5 +1,6 @@
 goog.provide('ol.parser.XML');
 
+goog.require('goog.dom.xml');
 goog.require('ol.parser.Parser');
 
 
@@ -246,3 +247,27 @@ ol.parser.XML.prototype.setAttributeNS = function(node, uri, name, value) {
     }
   }
 };
+
+
+/**
+ * Serializes a node.
+ *
+ * @param {Element} node Element node to serialize.
+ * @return {string} The serialized XML string.
+ */
+ol.parser.XML.prototype.serialize = function(node) {
+  if (node.nodeType == 1) {
+    // Add nodes to a document before serializing. Everything else
+    // is serialized as is. This is also needed to get all namespaces
+    // defined in some browsers such as Chrome (xmlns attributes).
+    var doc = document.implementation.createDocument('', '', null);
+    if (doc.importNode) {
+      doc.appendChild(doc.importNode(node, true));
+    } else {
+      doc.appendChild(node);
+    }
+    return goog.dom.xml.serialize(doc);
+  } else {
+    return goog.dom.xml.serialize(node);
+  }
+};