DevTools: [CodeMirror] fix coordinates-to-position implementation

This patch fixes the pixel coordinates to text position function
which is responsible for the popover target.

BUG=265521

Review URL: https://chromiumcodereview.appspot.com/21104004

git-svn-id: svn://svn.chromium.org/blink/trunk@155160 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Node.contains should return true for nodes in Shadow DOM.

This is discussed on this W3 bug:
<https://www.w3.org/Bugs/Public/show_bug.cgi?id=22141>

BUG=265697

Review URL: https://chromiumcodereview.appspot.com/21123005

git-svn-id: svn://svn.chromium.org/blink/trunk@155161 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Order of actions for labeled control should be focus then click.

When we click on a checkbox or a radio button, event order is:
 - mousedown
 - focus, triggered by mousedown
 - mouseup
 - change, triggered by the following click <wkbug.com/93674>
 - click

That is to say, we focus on it first and then click it. Click on an
associated label should have same behavior.

BUG=264567

Review URL: https://chromiumcodereview.appspot.com/21005002

git-svn-id: svn://svn.chromium.org/blink/trunk@155162 bbb929c8-8fbe-4397-9dbb-9b2b20218538