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

The spec now requires that when a URLSearchParams is initialized from
a string, an initial '?' should be ignored from that string,

 https://url.spec.whatwg.org/#dom-urlsearchparams-urlsearchparams

It accommodating usage like (new URLSearchParams(url.search))

R=
BUG=601425

Review URL: https://codereview.chromium.org/1906773002

Cr-Commit-Position: refs/heads/master@{#388842}
2 files changed