Remove gyp_cef and use gyp_chromium instead (issue #1304).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1740 5089003a-bbd8-11dd-ad1f-f1f9622dbc98
Update to Chromium revision 275973.

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1743 5089003a-bbd8-11dd-ad1f-f1f9622dbc98
Fix execution of OnBeforePluginLoad (issue #1284).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1744 5089003a-bbd8-11dd-ad1f-f1f9622dbc98