Revert 184074 "The link shoud be activated by enter key on focus..."

This caused interactive_ui_tests WebViewInteractiveTest.NewWindow_OpenInNewTab
always fail on many bots (Win7 dbg, Mac 10.6/10.8, Linux, Chrome OS) and prevented
Blink CLs to roll to chromium.

Please investigate why the test above fails with this change.

> The link shoud be activated by enter key on focusing the child element inside the anchor.
> This makes behaviour consistent with firefox and IE.
> 
> BUG=350738
> R=pdr@chromium.org
> TEST=LayoutTests/fast/events/keydown-enter-key-on-focused-element-inside-link.html
> 
> Review URL: https://codereview.chromium.org/619613005

TBR=myid.o.shin@gmail.com
BUG=425859

Review URL: https://codereview.chromium.org/662543007

git-svn-id: svn://svn.chromium.org/blink/trunk@184151 bbb929c8-8fbe-4397-9dbb-9b2b20218538