Single code path for updating invalidation sets.

Allow all selectors to update invalidation sets using updateInvalidationSets
and never fall back to a separate wholeSubtree loop in
collectFeaturesFromSelector. The method for finding the InvalidationSetMode
is dropped completely.

With this change we are now at a point were a whole subtree invalidation is
only necessary for these cases:

1. There are no recognized features in the rightmost compound selector

 - A universal selector: ".a *"
 - Only contains pseudo classes or elements that are not considered
   features:

   ".a ::before", ".a :first-child", etc.

2. The invalidation set component is immediately left of an adjacent
   combinator:

   ".a + .b", ".a ~ .b"

3. The selector has a ::first-letter or ::first-line pseudo

   These are currently depending on style recalc or layout below the
   element they are pseudo elements for.

3. There is a :host-context() in the rightmost compound selector

   :host-context sub-selectors match ascendants of the :host element for
   which we are resolving style, so ":host-context(.a)" is effectively the
   same as ".a :host" which falls under no recognized features in the
   rightmost compound in point 1.

Points 1, 3, and 4 are now handled through
InvalidationSetFeatures::forceSubtree set as a result of feature extraction.
Point 2 is handled by updating InvalidationSetFeatures::adjacent as we
progress past selector combinators.

RuleFeaturesSet::collectFeaturesFromSelector is now back to how it was
before we introduced invalidation sets (without the feature hash sets).
Now, it only counts adjacent combinators and sets a flag when finding
::first-line, so it is possible to squash it into the same method as
updateInvalidationSets() to have a single pass over the selector when
finding rule features (if we want to do that).

The lowered expected node count in the :host-context test is due to the
fact that we only fall back to subtree invalidation when present in the
rightmost compound. ::first-letter/::first-line are always in the rightmost
compound, and :host-context() doesn't need subtree invalidation when in
other compounds. ":host-context(.a) .b" is effectively ".a :host .b".

R=chrishtr@chromium.org
BUG=335247

Review URL: https://codereview.chromium.org/726503003

git-svn-id: svn://svn.chromium.org/blink/trunk@185354 bbb929c8-8fbe-4397-9dbb-9b2b20218538