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When the only things that changed are not tree boundary crossing rules we
can skip invalidation in descendant ShadowRoots. This means that
if you have lots of nested components with duplicate class names then using
a descendant selector in an enclosing component won't invalidate style in
nested ShadowRoots.

I also packed the booleans on DescendantInvalidationSet since we keep growing
it with new flags.

In the future we can make this tree boundary crossing logic even smarter so that
if you have both tree boundary and not tree boundary crossing invalidation
sets on the same subtree we can skip running the non-tree boundary crossing
rules when recursing into a ShadowRoot.

I also took this as an opportunity to clean up the addFeaturesToInvalidationSets
logic and merged the new treeBoundaryCrossing flag and the wholeSubtreeInvalid
flag into the InvalidationSetFeatures.

Review URL: https://codereview.chromium.org/286903024

git-svn-id: svn://svn.chromium.org/blink/trunk@175171 bbb929c8-8fbe-4397-9dbb-9b2b20218538