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CSSGlobalRuleSet should always be collected as part of the active style
update. RuleSets may have been cleared from StyleSheetContents as a
result of media query changes for instance.

For the given issue, we tried to limit to a global ruleset when lazy-
loading fullscreen UA style, but as part of going fullscreen we had
already cleared rule sets for stylesheets with media queries due to the
media feature change.

BUG=675439

Review-Url: https://codereview.chromium.org/2590793003
Cr-Commit-Position: refs/heads/master@{#439781}