Make date formatter available to plugins

Users can control via the user preferences how dates should be
formatted. Allow plugins to use the same date formatter as Gerrit core
that formats dates depending on the user preferences.

Note, we cannot simply move the complete FormatUtil class to
gerrit-gwtui-common because it needs access to the user preferences
and some server config, like the anonymous coward name, and this
information is retrieved differently in Gerrit core and plugins. This
is why for now we have 2 FormatUtil classes, one in Gerrit core and
one in gerrit-plugin-gwtui. Common parts such as the DateFormatter
will be made available to both FormatUtil classes by putting them into
gerrit-gwtui-common.

Change-Id: Iad241b461ad0171a2bbf279fb478dc40196cc201
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

gerrit-plugin-gwtui/src/main/java/com/google/gerrit/plugin/client/FormatUtil.java

@@ -0,0 +1,40 @@
+// Copyright (C) 2015 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.plugin.client;
+
+import com.google.gerrit.client.DateFormatter;
+
+import java.util.Date;
+
+public class FormatUtil {
+  /** Format a date using a really short format. */
+  public static String shortFormat(Date dt) {
+    return createDateFormatter().shortFormat(dt);
+  }
+
+  /** Format a date using a really short format. */
+  public static String shortFormatDayTime(Date dt) {
+    return createDateFormatter().shortFormatDayTime(dt);
+  }
+
+  /** Format a date using the locale's medium length format. */
+  public static String mediumFormat(Date dt) {
+    return createDateFormatter().mediumFormat(dt);
+  }
+
+  private static DateFormatter createDateFormatter() {
+    return new DateFormatter(Plugin.get().getUserPreferences());
+  }
+}