Revert 151179 "On IE and FireFox, they treats contenteditable="f..."

Revert 151179 "On IE and FireFox, they treats contenteditable="f..." 

> On IE and FireFox, they treats contenteditable="false" element as atomic element. When moving caret around it, cursor is placed at start/end of it. 
> 
> This patch changes Blink(Chrome) behavior as IE and FireFox. 
> 
> This patch updates tests for behavior change: 
> - editing/selection/4889598.html: Removed, because updated version of mixed-editability-3.html does same test, line motion around uneditable table element. 
> - editing/selection/mixed-editability-3.html: Changed to cover forward and backward line motion and verify by script rather than editing log and render tree for ease of future maintenance. 
> - editing/selection/move-by-line-004.html: Changed for new behavior. Caret can't go cross uneditable table cell as FireFox. 
> 
> BUG=238000
> 
> Review URL: https://chromiumcodereview.appspot.com/14794012 

NOTRY=true 
TBR=yosin@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=151185

[yosin_UTC9, 2013-05-27 09:09:56]

Committed patchset #1 manually as r151185 (presubmit successful).