Have (new URLSearchParams(initString)) skip initial '?'.

third_party/WebKit/LayoutTests/fast/domurl/urlsearchparams-constructor.html

Index: third_party/WebKit/LayoutTests/fast/domurl/urlsearchparams-constructor.html
diff --git a/third_party/WebKit/LayoutTests/fast/domurl/urlsearchparams-constructor.html b/third_party/WebKit/LayoutTests/fast/domurl/urlsearchparams-constructor.html
index 33a446e32332b7ce0cdd8c79d57ed0ff645dfe3b..9274ca5d2eab67ab3c9388175143c3761832cf39 100644
--- a/third_party/WebKit/LayoutTests/fast/domurl/urlsearchparams-constructor.html
+++ b/third_party/WebKit/LayoutTests/fast/domurl/urlsearchparams-constructor.html
@@ -33,6 +33,18 @@ test(function() {
     assert_equals(params + '', 'a=b');
     params = new URLSearchParams(params);
     assert_equals(params + '', 'a=b');
+
+    // Leading '?' should be ignored.
+    params = new URLSearchParams('?a=b');
+    assert_equals(params + '', 'a=b');
+
+    // Encoding '?' aligns with Firefox, spec doesn't insist it is encoded.

[philipj_slow, 2016/04/21 13:13:50]

'?' is 0x3F and I end up in
https://url.spec.whatwg.org/#concept-urlencoded-byte-serializer where that's one
of the code points that end up in "Append byte, percent encoded, to output."

Is there anything going on here that I'm missing, that might require a change to
the spec or some browser?

[sof, 2016/04/21 13:19:10]

You want to consider parsing first, I think --
https://url.spec.whatwg.org/#query-state

[philipj_slow, 2016/04/21 13:38:07]

Starting at the URLSearchParams constructor I end up in
https://url.spec.whatwg.org/#concept-urlencoded-parser where I can't see
anything special with '?', but I actually can't in "query state" either, AFAICT
one would end up in step 1.3.2 or 2.3, which just append.

What caught my attention was "spec doesn't insist", because if it isn't clear
per spec then I think Anne would consider that a bug. What's your reading of the
spec on this point?

+    params = new URLSearchParams('??a=b');
+    assert_equals(params + '', '%3Fa=b');
+    params = new URLSearchParams('?');
+    assert_equals(params + '', '');
+    params = new URLSearchParams('??');
+    assert_equals(params + '', '%3F=');
 }, 'Basic URLSearchParams construction');
 
 test(function() {