HTML5 Drag and Drop: Fire dragstart event during the drag and drop processing

Description: Fire dragstart event during the drag and drop processing

Test Result	Test Assertion
Manual	Test passes if if the word "PASS" appears to the left after following the steps below. Steps: Click and drag the red box

http://dev.w3.org/html5/spec/dnd.html#drag-and-drop-processing-model

If it is an element that is being dragged, then set the drag data store elements list to contain just the source node. Fire a DND event named dragstart at the source node.