Make logfile decoders accept a nested decoder instead of filename.

Change-Id: I4685d1dfbbd2bdd336762ee67471fa275883b772
Signed-off-by: Tyler Chatow <tyler.chatow@bluerivertech.com>
diff --git a/aos/events/logging/buffer_encoder.cc b/aos/events/logging/buffer_encoder.cc
index 10a7ed1..6ef61d4 100644
--- a/aos/events/logging/buffer_encoder.cc
+++ b/aos/events/logging/buffer_encoder.cc
@@ -39,7 +39,7 @@
 }
 
 DummyDecoder::DummyDecoder(std::string_view filename)
-    : fd_(open(std::string(filename).c_str(), O_RDONLY | O_CLOEXEC)) {
+    : filename_(filename), fd_(open(filename_.c_str(), O_RDONLY | O_CLOEXEC)) {
   PCHECK(fd_ != -1) << ": Failed to open " << filename;
 }