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The added sheets passed into StyleSheetInvalidationAnalysis may either be
added or removed. When they are removed style elements from a shadow tree,
the style element may no longer have a containingShadowRoot if the element
has already been removed. That caused a crash when the containingShadowRoot
was accessed without a nullptr check.

Instead of deducing the scope from the style element, pass the stylesheet
collection TreeScope to the analysis object. The m_scopingNodes, which is
probably a left-over from <style scoped> has been removed.

Now, the shadow tree root node, or outermost shadow host if ::content
rules makes that necessary, is always marked sub-tree dirty. The previous
code-path could trigger id/class invalidation of separate elements when
the stylesheet contents had multiple owner nodes, but that was most likely
wrong if it could ever happen.

BUG=522860

Review URL: https://codereview.chromium.org/1313443003

git-svn-id: svn://svn.chromium.org/blink/trunk@201058 bbb929c8-8fbe-4397-9dbb-9b2b20218538