Fix dynamically inserted media queries.

https://src.chromium.org/viewvc/blink?view=rev&revision=162573
caused dynamically inserted media queries to not apply
because insertRule would not mark the hasMediaQueries bit
on the StyleSheetContents.

With the current patch, if you add a media query and then remove
it, we'll erroneously think that the stylesheet still has media
queries, but that doesn't seem like a big deal to me. It doesn't
present as a bug. It just affects performance.

BUG=331899

Review URL: https://codereview.chromium.org/130123002

git-svn-id: svn://svn.chromium.org/blink/trunk@164825 bbb929c8-8fbe-4397-9dbb-9b2b20218538