Pull libxml2 into test_support_chromiumcontent

This is needed by Chromium's custom unit test runner.
Pull zlib into test_support_chromiumcontent

This is needed by libxml.
Pull base_static into test_support_chromiumcontent

This is needed for the kTestChildProcess switch. (base_static.pdb is
already included in the distribution.)
Merge pull request #35 from brightray/content-test-suite

Pull in dependencies to make content::ContentTestSuiteBase usable