Remove webrtc/stream.h and unutilized inheritance.

Removes inheritance and a virtual call. Also removes a root header that
would have needed to be moved into a subdirectory otherwise to prevent
circular dependencies.

BUG=webrtc:4243
R=kjellander@webrtc.org, solenberg@webrtc.org
TBR=mflodman@webrtc.org

Review-Url: https://codereview.webrtc.org/1924793002
Cr-Original-Commit-Position: refs/heads/master@{#12586}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 1ba8d39a9cee4d8771faa440ac4d2978170fc8ea
diff --git a/common_types.h b/common_types.h
index e171e1b..58aebdc 100644
--- a/common_types.h
+++ b/common_types.h
@@ -880,6 +880,11 @@
 // RTCP mode is described by RFC 5506.
 enum class RtcpMode { kOff, kCompound, kReducedSize };
 
+enum NetworkState {
+  kNetworkUp,
+  kNetworkDown,
+};
+
 }  // namespace webrtc
 
 #endif  // WEBRTC_COMMON_TYPES_H_