embedding: fix string_list deallocation where I accidentally the whole string_list
embedding: fix string_list compile errors?
embedding: add string_map_to_vec() to reduce transmute calls
auto merge of #3785 : zmike/servo/embedding-fixups-for-string_list, r=larsbergstrom

r+ @jdm @larsbergstrom  ?
Fix build warnings in the cef port.
Make some warnings errors in the cef port.