TextEvent: inputMode with DOM_INPUT_METHOD_DROP

### DOM Events

#### Test Description: TextEvent.inputMode is DOM_INPUT_METHOD_DROP (0x03) when the text string was inserted as part of a drag-and-drop operation.

Hello World

Steps:

1. Select "Hello World" inside the green editbox
2. Drag-and-drop it ("Hello World") to the textbox below the green editbox

Test passes if the word "PASS" appears below after following the above steps.

Test result:
FAIL