Move AudioDecoderIsac* to its own files

webrtc/modules/audio_coding/BUILD.gn

Index: webrtc/modules/audio_coding/BUILD.gn
diff --git a/webrtc/modules/audio_coding/BUILD.gn b/webrtc/modules/audio_coding/BUILD.gn
index 5d85db3e1a451734b01b0c95dcbc532c8431cd78..5725ec03df4d5be9cbb5c8087793f29ad0de436a 100644
--- a/webrtc/modules/audio_coding/BUILD.gn
+++ b/webrtc/modules/audio_coding/BUILD.gn
@@ -412,12 +412,14 @@ config("isac_config") {
 
 source_set("isac") {
   sources = [
+    "codecs/isac/main/interface/audio_decoder_isac.h",
     "codecs/isac/main/interface/audio_encoder_isac.h",
     "codecs/isac/main/interface/isac.h",
     "codecs/isac/main/source/arith_routines.c",
     "codecs/isac/main/source/arith_routines.h",
     "codecs/isac/main/source/arith_routines_hist.c",
     "codecs/isac/main/source/arith_routines_logist.c",
+    "codecs/isac/main/source/audio_decoder_isac.cc",
     "codecs/isac/main/source/audio_encoder_isac.cc",
     "codecs/isac/main/source/bandwidth_estimator.c",
     "codecs/isac/main/source/bandwidth_estimator.h",
@@ -439,6 +441,7 @@ source_set("isac") {
     "codecs/isac/main/source/filterbanks.c",
     "codecs/isac/main/source/intialize.c",
     "codecs/isac/main/source/isac.c",
+    "codecs/isac/main/source/isac_float_type.h",
     "codecs/isac/main/source/lattice.c",
     "codecs/isac/main/source/lpc_analysis.c",
     "codecs/isac/main/source/lpc_analysis.h",
@@ -493,12 +496,14 @@ config("isac_fix_config") {
 
 source_set("isac_fix") {
   sources = [
+    "codecs/isac/fix/interface/audio_decoder_isacfix.h",
     "codecs/isac/fix/interface/audio_encoder_isacfix.h",
     "codecs/isac/fix/interface/isacfix.h",
     "codecs/isac/fix/source/arith_routines.c",
     "codecs/isac/fix/source/arith_routines_hist.c",
     "codecs/isac/fix/source/arith_routines_logist.c",
     "codecs/isac/fix/source/arith_routins.h",
+    "codecs/isac/fix/source/audio_decoder_isacfix.cc",
     "codecs/isac/fix/source/audio_encoder_isacfix.cc",
     "codecs/isac/fix/source/bandwidth_estimator.c",
     "codecs/isac/fix/source/bandwidth_estimator.h",
@@ -516,6 +521,7 @@ source_set("isac_fix") {
     "codecs/isac/fix/source/filterbanks.c",
     "codecs/isac/fix/source/filters.c",
     "codecs/isac/fix/source/initialize.c",
+    "codecs/isac/fix/source/isac_fix_type.h",
     "codecs/isac/fix/source/isacfix.c",
     "codecs/isac/fix/source/lattice.c",
     "codecs/isac/fix/source/lattice_c.c",