Added dart:js samples landing pages.

src/site/samples/google_maps/index.markdown

+---
+layout: default
+title: Google Maps API and dart:js
+live_example_url: example/index.html
+
+header:
+  css: ["/samples/samples.css"]
+---
+
+## {{ page.title }}
+
+This code derives from a Google Maps JavaScript API
+[Hello World]( https://developers.google.com/maps/documentation/javascript/tutorial#HelloWorld)
+example. The example uses the `dart:js` library for Dart and JavaScript
+interoperability.
+
+See the
+[original
+example](https://developers.google.com/maps/documentation/javascript/examples/map-simple).
+
+Read the [dart:js API
+docs](http://api.dartlang.org/docs/releases/latest/dart_js.html).
+
+Read the
+[source](https://code.google.com/p/dart/source/browse/#svn%2Fbranches%2Fbleeding_edge%2Fdart%2Fsamples%2Fgoogle_maps).
+
+<iframe class="running-app-frame"
+        style="height:500px;width:100%;"
+        src="{{page.live_example_url}}">
+</iframe>
+
+See all [samples](/samples/)