Allow setContentDecryptionModule() to get called when setting is done.

media/filters/decrypting_demuxer_stream.cc

Index: media/filters/decrypting_demuxer_stream.cc
diff --git a/media/filters/decrypting_demuxer_stream.cc b/media/filters/decrypting_demuxer_stream.cc
index 4ec6c530b2411efdbb170350c544a22dfa687e7a..67a6f3e77ae0a5d6232f68b31d6958513807f47d 100644
--- a/media/filters/decrypting_demuxer_stream.cc
+++ b/media/filters/decrypting_demuxer_stream.cc
@@ -160,7 +160,8 @@ DecryptingDemuxerStream::~DecryptingDemuxerStream() {
   pending_buffer_to_decrypt_ = NULL;
 }
 
-void DecryptingDemuxerStream::SetDecryptor(Decryptor* decryptor) {
+void DecryptingDemuxerStream::SetDecryptor(Decryptor* decryptor,
+                                           base::Closure done_cb) {
   DVLOG(2) << __FUNCTION__;
   DCHECK(task_runner_->BelongsToCurrentThread());
   DCHECK_EQ(state_, kDecryptorRequested) << state_;
@@ -172,6 +173,8 @@ void DecryptingDemuxerStream::SetDecryptor(Decryptor* decryptor) {
   if (!decryptor) {
     state_ = kUninitialized;
     base::ResetAndReturn(&init_cb_).Run(DECODER_ERROR_NOT_SUPPORTED);
+    if (!done_cb.is_null())
+      done_cb.Run();
     return;
   }
 
@@ -184,6 +187,8 @@ void DecryptingDemuxerStream::SetDecryptor(Decryptor* decryptor) {
 
   state_ = kIdle;
   base::ResetAndReturn(&init_cb_).Run(PIPELINE_OK);
+  if (!done_cb.is_null())
+    done_cb.Run();
 }
 
 void DecryptingDemuxerStream::DecryptBuffer(