Split sdch_manager_unittest.cc out of sdch_filter_unittest.cc

BUG=313716

Review URL: https://codereview.chromium.org/134903002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244552 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244552