Revert 158866 "@page rule missing from simpleUserAgentStyleSheet."

This CL broke the following browser tests:

PrintWebViewHelperPreviewTest.PrintPreviewShrinkToFitPage
PrintWebViewHelperPreviewTest.PrintPreviewCenterToFitPage

See http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&testType=browser_tests&tests=PrintWebViewHelperPreviewTest.PrintPreviewShrinkToFitPage,PrintWebViewHelperPreviewTest.PrintPreviewCenterToFitPage


> @page rule missing from simpleUserAgentStyleSheet.
> 
> simpleUserAgentStyleSheet did not have an @page rule like html.css.
> The result was flakiness for the following test depending on whether the full
> UA styles had been triggered by a previous test or not:
> 
> LayoutTests/printing/page-format-data.html
> 
> R=ojan
> BUG=303324
> 
> Review URL: https://codereview.chromium.org/25856002

TBR=rune@opera.com

Review URL: https://codereview.chromium.org/25677008

git-svn-id: svn://svn.chromium.org/blink/trunk@158888 bbb929c8-8fbe-4397-9dbb-9b2b20218538