Add gyp and gn targets for jFormatString.jar needed by errorprone.

findbugs.gyp

Index: findbugs.gyp
diff --git a/findbugs.gyp b/findbugs.gyp
new file mode 100644
index 0000000000000000000000000000000000000000..584f1236caddcd38467a0df5e8476d01653bd762
--- /dev/null
+++ b/findbugs.gyp
@@ -0,0 +1,19 @@
+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+{
+  'targets': [
+    {
+      # GN: //third_party/findbugs:format_string_java
+      'target_name': 'format_string_jar',
+      'type': 'none',
+      'variables': {
+        'jar_path': 'lib/jFormatString.jar',
+      },
+      'includes': [
+        '../../build/host_prebuilt_jar.gypi',
+      ]
+    },
+  ]
+}