Adding `content_security_policy` to the "Mappy" sample.

chrome/common/extensions/docs/examples/extensions/mappy/popup.css

Index: chrome/common/extensions/docs/examples/extensions/mappy/popup.css
diff --git a/chrome/common/extensions/docs/examples/extensions/mappy/popup.css b/chrome/common/extensions/docs/examples/extensions/mappy/popup.css
new file mode 100644
index 0000000000000000000000000000000000000000..809178813ea5b9b47f2b961df9f233956ba574b1
--- /dev/null
+++ b/chrome/common/extensions/docs/examples/extensions/mappy/popup.css
@@ -0,0 +1,15 @@
+/**
+ * Copyright (c) 2011 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.
+ */
+
+body {
+  margin: 0px;
+  padding: 0px;
+}
+
+#map {
+  width: 512px;
+  height: 512px;
+}