Fix a regression when editor does not restore scroll position when switching tabs.

R=pfeldman, lushnikov, apavlov

Review URL: https://chromiumcodereview.appspot.com/21764003

git-svn-id: svn://svn.chromium.org/blink/trunk@155437 bbb929c8-8fbe-4397-9dbb-9b2b20218538