adb: add dry-run option to push/sync.

Make it easier to benchmark file sync performance by ignoring the file
system.

Bug: https://issuetracker.google.com/150827486
Test: test_device.py
Change-Id: Icfa4b28eb5206f1914c0c163833d070a3748c3ea
diff --git a/transport.h b/transport.h
index 12803b5..4b2e000 100644
--- a/transport.h
+++ b/transport.h
@@ -90,6 +90,8 @@
 extern const char* const kFeatureSendRecv2Brotli;
 // adbd supports LZ4 for send/recv v2.
 extern const char* const kFeatureSendRecv2LZ4;
+// adbd supports dry-run send for send/recv v2.
+extern const char* const kFeatureSendRecv2DryRunSend;
 
 TransportId NextTransportId();