DevTools: do not force excessive layout on every change in editor
DevTools: do not force excessive layout on every change in editor

This patch makes TabbedPane.setTabIcon to result in noop if
the icon is already set.

BUG=321735

Review URL: https://codereview.chromium.org/83483011

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@162579 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs