AudioCodingModule::Create(): Require caller to supply an AudioDecoderFactory

So that we don't have to be capable of creating one ourselves, which
requires a dependency on the audio decoders.

BUG=webrtc:5801, webrtc:8396

Change-Id: I80749ec3b86cba73994307046d05964f59167d44
Reviewed-on: https://webrtc-review.googlesource.com/18440
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Oskar Sundbom <ossu@webrtc.org>
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22774}

modules/audio_coding/test/target_delay_unittest.cc

@@ -10,6 +10,7 @@
 
 #include <memory>
 
+#include "api/audio_codecs/builtin_audio_decoder_factory.h"
 #include "common_types.h"  // NOLINT(build/include)
 #include "modules/audio_coding/codecs/pcm16b/pcm16b.h"
 #include "modules/audio_coding/include/audio_coding_module.h"
@@ -22,7 +23,9 @@ namespace webrtc {
 
 class TargetDelayTest : public ::testing::Test {
  protected:
-  TargetDelayTest() : acm_(AudioCodingModule::Create()) {}
+  TargetDelayTest()
+      : acm_(AudioCodingModule::Create(
+            AudioCodingModule::Config(CreateBuiltinAudioDecoderFactory()))) {}
 
   ~TargetDelayTest() {}