Propagate ozone platform flag to the GPU process

When running with the GPU process SurfaceFactoryOzone is initialized and used
by the GPU process. In order to create the appropriate SurfaceFactoryOzone
implementation we need to propagate the ozone platform to the GPU process.

BUG=

Review URL: https://codereview.chromium.org/108813002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239504 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239504