Use StringUTF8Adaptor in KURL::operator GURL

This can save a conversion to UTF-8 (and copy to CString) for ASCII-only
URLs.

Bug: 889183
Change-Id: Ie5edad4a95da70bac0acd27b01d6e03cd1315bbd
Reviewed-on: https://chromium-review.googlesource.com/c/1257926
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596192}

third_party/blink/renderer/platform/weborigin/kurl.cc

@@ -874,7 +874,8 @@ bool KURL::IsSafeToSendToAnotherThread() const {
 }
 
 KURL::operator GURL() const {
-  return GURL(string_.Utf8().data(), parsed_, is_valid_);
+  StringUTF8Adaptor utf8(string_);
+  return GURL(utf8.Data(), utf8.length(), parsed_, is_valid_);
 }
 
 }  // namespace blink