DevTools: screencast: request image in dip, not css for high zoom factors.

R=kaznacheev@chromium.org

Review URL: https://codereview.chromium.org/70193009

git-svn-id: svn://svn.chromium.org/blink/trunk@161938 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Process treeBoundaryCrossingRules in a post-step outside of RuleData.

This is another step in making it so that RuleSets
don't need to know about scoping nodes or StyleResolvers.

Unfortunately, TreeBoundaryCrossingRules::addRule needs to take
a non-const ContainerNode*, which meant I had to remove the const
qualifiers from a bunch of places.

BUG=311669

Review URL: https://codereview.chromium.org/70623003

git-svn-id: svn://svn.chromium.org/blink/trunk@161939 bbb929c8-8fbe-4397-9dbb-9b2b20218538