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: svn://svn.chromium.org/blink/trunk@162579 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[websql] don't directly expose the thread id on the database thread

BUG=301514
R=michaeln@chromium.org

Review URL: https://codereview.chromium.org/83593002

git-svn-id: svn://svn.chromium.org/blink/trunk@162580 bbb929c8-8fbe-4397-9dbb-9b2b20218538