Update DOMString url types with USVString in the NavigatorContentUtils.idl

Latest spec has used USVString instead of DOMString for url argument.
 - spec: https://html.spec.whatwg.org/multipage/system-state.html#custom-handlers

This CL replaces DOMString type with USVString type according to the spec.

Bug: 790860
Change-Id: I179144780bd345bc71e9b9beeaea3470a8e3d302
Reviewed-on: https://chromium-review.googlesource.com/781320Reviewed-by: Takeshi Yoshino <tyoshino@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: Gyuyoung Kim <gyuyoung.kim@lge.com>
Cr-Commit-Position: refs/heads/master@{#522081}

third_party/WebKit/Source/modules/navigatorcontentutils/NavigatorContentUtils.idl

@@ -23,6 +23,6 @@
 [
     ImplementedAs=NavigatorContentUtils
 ] partial interface Navigator {
-    [RuntimeEnabled=NavigatorContentUtils, RaisesException] void registerProtocolHandler(DOMString scheme, DOMString url, DOMString title);
-    [RuntimeEnabled=NavigatorContentUtils, RaisesException] void unregisterProtocolHandler(DOMString scheme, DOMString url);
+    [RuntimeEnabled=NavigatorContentUtils, RaisesException] void registerProtocolHandler(DOMString scheme, USVString url, DOMString title);
+    [RuntimeEnabled=NavigatorContentUtils, RaisesException] void unregisterProtocolHandler(DOMString scheme, USVString url);
 };