Remove the media query expressions serialization cache

It is not needed as the expressions are not individually
accessible from CSSOM, and I suppose the cache only existed
as the serialization was done twice during creating of the
MediaQuery object. That is not needed as you can compare
the MediaQueryExp directly.

R=apavlov@chromium.org

Review URL: https://codereview.chromium.org/15715022

git-svn-id: svn://svn.chromium.org/blink/trunk@151653 bbb929c8-8fbe-4397-9dbb-9b2b20218538
3 files changed