Reland "Add first part of the network_tester functionality"

webrtc/tools/network_tester/network_tester_packet.proto

Index: webrtc/tools/network_tester/network_tester_packet.proto
diff --git a/webrtc/tools/network_tester/network_tester_packet.proto b/webrtc/tools/network_tester/network_tester_packet.proto
new file mode 100644
index 0000000000000000000000000000000000000000..c3bcec5ec7003edbbfadc8fd60312e67db984d1e
--- /dev/null
+++ b/webrtc/tools/network_tester/network_tester_packet.proto
@@ -0,0 +1,18 @@
+syntax = "proto2";
+option optimize_for = LITE_RUNTIME;
+package webrtc.network_tester.packet;
+
+message NetworkTesterPacket {
+  enum Type {
+    HAND_SHAKING = 0;
+    TEST_START = 1;
+    TEST_DATA = 2;
+    TEST_DONE = 3;
+  }
+
+  optional Type type = 1;
+  optional int64 send_timestamp = 2;
+  optional int64 arrival_timestamp = 3;
+  optional int64 sequence_number = 4;
+  optional int32 packet_size = 5;
+}