When dragging a selection, clearing the selection in dragstart should not crash the web process

[Wenson Hsieh]

Test case:

<meta name="viewport" content="width=device-width, initial-scale=1">
<code><p id="paragraph" style="font-size: 100px;">START DRAGGING</p></code>
<script>
function select(node) {
    let range = document.createRange(node);
    range.setStartBefore(node);
    range.setEndAfter(node);
    getSelection().removeAllRanges();
    getSelection().addRange(range);
}

select(paragraph.childNodes[0]);
document.body.addEventListener("dragstart", () => {
    getSelection().removeAllRanges();
    paragraph.textContent = "PASS";
    paragraph.style.color = "green";
});
</script>

[Wenson Hsieh]

<rdar://problem/33067501>

[Wenson Hsieh]

Created attachment 314586 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 314586 [details]
Patch

Clearing flags on attachment: 314586

Committed r219153: <http://trac.webkit.org/changeset/219153>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.