Clean up mojo export files.

While I was looking at these files I noticed the GFX_IMPLEMENTATION,
which triggered me to make these cleanups.

BUG=None
TEST=None
TBR=darin@chromium.org

Review URL: https://codereview.chromium.org/110843003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240009 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240009
Split net::ClientCertStoreImpl into actual platform-specific classes.

BUG=none

Review URL: https://codereview.chromium.org/108233005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@240010 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 240010