Added landing pages for new samples

src/site/samples/dndfiles/index.markdown

Index: src/site/samples/dndfiles/index.markdown
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+---

[Kathy Walrath, 2013/10/23 15:41:05]

dndfiles/ -> dnd-files/?

(for SEO and consistency of directory names on this site)

[shailentuli, 2013/10/23 17:36:57]

I'm keeping the naming exactly the same as it is in the HTML5Rocks article and
url.  I suggest leaving this as dndfiles.

+layout: default
+title: HTML5 Drag and Drop files

[Kathy Walrath, 2013/10/23 15:41:05]

files -> Files

[shailentuli, 2013/10/23 17:36:57]

Done.

+live_example_url: example/index.html
+
+header:
+  css: ["/samples/samples.css"]
+---
+
+## {{ page.title }}
+
+A port of the Drag and Drop Files example used in the
+[Native HTML5 Drag and Drop](http://www.html5rocks.com/en/tutorials/dnd/basics/)
+article by Eric Bidelman, originally published on HTML5Rocks.
+
+HTML5 Drag and drop (DnD) is event-based way of making an element draggable

[Kathy Walrath, 2013/10/23 15:41:05]

is -> is an

[shailentuli, 2013/10/23 17:36:57]

Done.

+on a page. Native browser support for this feature means faster, more
+responsive web apps. With the DnD APIs, it is possible to drag files from
+the desktop to your web app in the browser window.

[Kathy Walrath, 2013/10/23 15:41:05]

This example is a little weird. Is it true that only the first "example" shows
DnD? (I saw only a file chooser in the other 2 examples.)

[shailentuli, 2013/10/23 17:36:57]

You are correct. I'm moving this under the File API category, with a link from
the D&D category.

+
+You can open the example in Dart Editor and run it by clicking `index.html`.
+
+Read the
+[source](https://github.com/dart-lang/dart-samples/tree/master/web/html5/file/dndfiles).
+
+<iframe class="running-app-frame"
+        style="height:500px;width:100%;"
+        src="{{page.live_example_url}}">
+</iframe>
+
+See all [samples](/samples/).