Upgrade webauth from deprecated base::JSONReader API

Bug: 1070409
Change-Id: I37e8de608a75dbbfc1fcb576cab0b0db3e50c2e0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2212230Reviewed-by: Martin Kreichgauer <martinkr@google.com>
Commit-Queue: Nigel Tao <nigeltao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772025}

content/browser/webauth/webauth_browsertest.cc

@@ -1136,8 +1136,8 @@ base::Optional<std::string> ExecuteScriptAndExtractPrefixedString(
       return base::nullopt;
     }
 
-    base::JSONReader reader(base::JSON_ALLOW_TRAILING_COMMAS);
-    std::unique_ptr<base::Value> result = reader.ReadToValueDeprecated(json);
+    base::Optional<base::Value> result =
+        base::JSONReader::Read(json, base::JSON_ALLOW_TRAILING_COMMAS);
     if (!result) {
       return base::nullopt;
     }