Add URLSearchParams.prototype.sort()

This method is added to increase cache hits when making requests. It’s
opt-in as the order of code points in a URL’s query is significant by
default. It’s up to applications to decide if name order is not
significant for them.

Tests: web-platform-tests/wpt#4531.

Fixes #26.

url.bs

@@ -2765,6 +2765,9 @@ interface URLSearchParams {
   sequence<USVString> getAll(USVString name);
   boolean has(USVString name);
   void set(USVString name, USVString value);
+
+  void sort();
+
   iterable<USVString, USVString>;
   stringifier;
 };
@@ -2843,6 +2846,11 @@ method, when invoked, must return the value of the first name-value pair whose n
 method, when invoked, must return the values of all name-value pairs whose name is <var>name</var>,
 in <a for=URLSearchParams>list</a>, in list order, and the empty sequence otherwise.
 
+<p>The
+<dfn method for=URLSearchParams><code>has(<var>name</var>)</code></dfn>
+method, when invoked, must return true if there is a name-value pair whose name is <var>name</var>
+in <a for=URLSearchParams>list</a>, and false otherwise.
+
 <p>The
 <dfn method for=URLSearchParams><code>set(<var>name</var>, <var>value</var>)</code></dfn>
 method, when invoked, must run these steps:
@@ -2858,10 +2866,19 @@ method, when invoked, must run these steps:
  <li><p>Run the <a for=URLSearchParams>update steps</a>.
 </ol>
 
-<p>The
-<dfn method for=URLSearchParams><code>has(<var>name</var>)</code></dfn>
-method, when invoked, must return true if there is a name-value pair whose name is <var>name</var>
-in <a for=URLSearchParams>list</a>, and false otherwise.
+<hr>
+
+<p>The <dfn method for=URLSearchParams><code>sort()</code></df> method, when invoked, must run these
+steps:
+
+<ol>
+ <li><p>Lexicographically sort all name-value pairs, if any, by name, while preserving the relative
+ order between duplicate names, if any.
+
+ <li><p>Run the <a for=URLSearchParams>update steps</a>.
+</ol>
+
+<hr>
 
 <p>The <a>value pairs to iterate over</a> are the
 <a for=URLSearchParams>list</a> name-value pairs with the key being