* Added aec_core_internal.h for private variables.
* Moved aec_t struct to aec_core_internal.h
* Name change aec_t -> AecCore
* Moved additional declarations to aec_core_internal.h
* Tested with audioproc_unittest and trybots
TEST=none
BUG=none
Review URL: https://webrtc-codereview.appspot.com/1117004
git-svn-id: http://webrtc.googlecode.com/svn/trunk@3553 4adac7df-926f-26a2-2b94-8c16560cd09d