DevTools: lock panel switching when timeline is active.

Drive by: fix exception in Counters code.

BUG=381115

Review URL: https://codereview.chromium.org/345803003

git-svn-id: svn://svn.chromium.org/blink/trunk@176855 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Outline ContentSecurityPolicy::document()

This allows the Document.h include to be removed from
ContentSecurityPolicy.h, which reduces recompilation when
touching Document.h from 1156 to 1101 steps locally.

Since document() was only used internally, make it private.

Review URL: https://codereview.chromium.org/348743006

git-svn-id: svn://svn.chromium.org/blink/trunk@176856 bbb929c8-8fbe-4397-9dbb-9b2b20218538
block-layout-inline-children-replaced.html is flaky.

TBR=leviw@chromium.org
BUG=320139

Review URL: https://codereview.chromium.org/358463002

git-svn-id: svn://svn.chromium.org/blink/trunk@176857 bbb929c8-8fbe-4397-9dbb-9b2b20218538