Inserting list item when typing Enter in list item containing paragraph

This patch changes behavior of InsertParagraphSeparator command when inserting paragraph separator into list item containing paragraph to insert paragraph separator with clone of enclosing list item.

This new behavior is specified in the latest, May 20, 2012 version of HTML Editing specification and compatible with IE and FireFox.

BUG=224709, 222918
TEST=LayoutTests/editing/inserting/insert-paragraph-separator-in-paragraph-in-list.html
R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/19749002

git-svn-id: svn://svn.chromium.org/blink/trunk@158070 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Revert r158037 - "Move FontSelector to StyleEngine."

This change caused a failure in content_browsertests under ASAN
(a use-after-free in ~CSSFontSelector).

See http://build.chromium.org/p/chromium.memory/builders/Linux%20ASAN%20Tests%20%282%29/builds/17540/steps/browser_tests/logs/stdio

Original code review: https://chromiumcodereview.appspot.com/23464076

TBR=dglazkov@chromium.org, kkania@chromium.org, japhet@chromium.org, simonhatch@chromium.org, eseidel@chromium.org
BUG=291287

Review URL: https://codereview.chromium.org/24257007

git-svn-id: svn://svn.chromium.org/blink/trunk@158071 bbb929c8-8fbe-4397-9dbb-9b2b20218538