Remove --enable-per-tile-painting and --ui-enable-per-tile-painting.

The ui flag is always true on ChromeOS and off elsewhere. The other is
never on and we're not planning to turn it on.

R=piman
BUG=

Review URL: https://codereview.chromium.org/164183012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251538 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251538