Ignore JdkObsolete issue with StringBuffer

HttpServletRequest#getRequestURL() returns the obsolete StringBuffer
class. Add a util method to get the requets URL as String that allows us
to ignore the JdkObsolete issue.

Bug: Issue 15070
Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I0dad2e4c2276088b7fffdfadfca7f24c553f5fd2

src/main/java/com/googlesource/gerrit/plugins/gitiles/MenuFilter.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/gitiles/MenuFilter.java b/src/main/java/com/googlesource/gerrit/plugins/gitiles/MenuFilter.java
index 1fd26e2..263fd70 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/gitiles/MenuFilter.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/gitiles/MenuFilter.java
@@ -68,7 +68,7 @@
   private String getLoginRedirectUrl(HttpServletRequest req) {
     String baseUrl = urls.getBaseGerritUrl(req);
     String loginUrl = baseUrl + "login/";
-    String token = req.getRequestURL().toString();
+    String token = getRequestUrl(req);
     if (!baseUrl.isEmpty()) {
       token = token.substring(baseUrl.length());
     }
@@ -79,4 +79,9 @@
     }
     return (loginUrl + Url.encode(token));
   }
+
+  @SuppressWarnings("JdkObsolete")
+  private static String getRequestUrl(HttpServletRequest req) {
+    return req.getRequestURL().toString();
+  }
 }