Implement URLSearchParams.

LayoutTests/fast/dom/HTMLAnchorElement/set-href-attribute-searchParams-expected.txt

+Test handling of the searchParams attribute of the URL in HTMLAnchorElement.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+Inspect single name-value via searchParams
+PASS a.searchParams.has('key') is true
+PASS a.searchParams.get('key') is "value"
+PASS a.href is "https://www.mydomain.com/path/?key=value"
+Add name-value pair using searchParams
+PASS a.searchParams.has('k e y') is true
+PASS a.searchParams.get('k e y') is "value"
+PASS a.search is "?k+e+y=value"
+PASS a.href is "https://www.mydomain.com/path/?k+e+y=value"
+Update name-value pair using searchParams
+PASS a.searchParams.has('key') is true
+PASS a.searchParams.get('key') is "newvalue"
+PASS a.search is "?key=newvalue"
+PASS a.href is "https://www.mydomain.com/path/?key=newvalue"
+Remove name-value pair using searchParams
+PASS a.searchParams.has('key') is false
+PASS a.search is ""
+PASS a.href is "https://www.mydomain.com/path/?"
+Have searchParams reflect removed name-value pairs
+PASS searchParams.has('key') is true
+PASS searchParams.has('key') is false
+PASS a.href is "https://www.mydomain.com/path/?"
+PASS successfullyParsed is true
+
+TEST COMPLETE
+