Build WebRTC with data channel only.

webrtc/logging/rtc_event_log/rtc_event_log.h

Index: webrtc/logging/rtc_event_log/rtc_event_log.h
diff --git a/webrtc/logging/rtc_event_log/rtc_event_log.h b/webrtc/logging/rtc_event_log/rtc_event_log.h
index bb4cc2e781fbfc89719cfbebed96e9b739f13eda..f23beaa9e048a985c075c8e823fbff1be36d951e 100644
--- a/webrtc/logging/rtc_event_log/rtc_event_log.h
+++ b/webrtc/logging/rtc_event_log/rtc_event_log.h
@@ -15,6 +15,7 @@
 #include <string>
 #include <vector>
 
+#include "webrtc/base/logging.h"
 #include "webrtc/base/platform_file.h"
 #include "webrtc/config.h"
 
@@ -189,7 +190,13 @@ class RtcEventLogNullImpl : public RtcEventLog {
     return false;
   }
   bool StartLogging(rtc::PlatformFile platform_file,
-                    int64_t max_size_bytes) override;
+                    int64_t max_size_bytes) override {
+    // The platform_file is open and needs to be closed.

[the sun, 2017/06/05 14:27:15]

The best solution would be to declare the interface in rtc_event_log.h, then
have two separate .h files for the Create() methods - one for the null impl, one
for the "true" impl. The two .h and their corresponding .cc files would then
live in separate build targets and there would be no need for doing work in this
.h file.

This is a minor comment in this context, though.

[Zhi Huang, 2017/06/06 03:09:51]

I agree that separating the interface and the subclass implementation is a
better solution.

I think what we need here is moving the implementation of RtcEventLogNullImpl
out of target "rtc_event_log_impl" so that we can depend on this without
introducing other unnecessary stuff. We can do this by either moving the
nullimpl to rtc_event_log_api or making a separate target like
"rtc_event_log_null_impl". 

Firstly, I don't think we can move the declaration of RtcEventLogNullImpl out of
this header because the internal project is depending on the RtcEventLogNullImpl
through this header and we don't want the interface header to depend on the
implementation header either. So we cannot easily have a separate target for the
impl and we need to move the impl to api target instead. 

Beside what I have done here, what we can do is having an rtceventlognullimpl.cc
which implements the RtcEventLogNullImpl and making the "rtc_event_log_api"
target depend on this .cc file to avoid linking error. I can do that if that
looks better to you.

[skvlad, 2017/06/06 17:49:21]

I think putting the function inline into the header is a good tradeoff to avoid
introducing another file for the null implementation (which would be a small but
breaking change for existing users). Especially since all our other functions
are already inline.

+    if (!rtc::ClosePlatformFile(platform_file)) {
+      LOG(LS_ERROR) << "Can't close file.";
+    }
+    return false;
+  }
   void StopLogging() override {}
   void LogVideoReceiveStreamConfig(
       const rtclog::StreamConfig& config) override {}