Add PrintedPage::GetCenteredPageContentRect so Mac and Win can share code.

BUG=47277
TEST=printed_page_unittest

Review URL: http://codereview.chromium.org/2878022

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@51626 0039d316-1c4b-4281-b951-d872f2087c98
6 files changed