Add CowWriter interface methods to DynamicPartiitonControl

Test: treehugger
Change-Id: I110c65e75a4594af51e68390e570ac31b50de8b5
diff --git a/common/dynamic_partition_control_stub.cc b/common/dynamic_partition_control_stub.cc
index c63a8ff..64ab201 100644
--- a/common/dynamic_partition_control_stub.cc
+++ b/common/dynamic_partition_control_stub.cc
@@ -20,6 +20,7 @@
 #include <string>
 
 #include <base/logging.h>
+#include <libsnapshot/cow_writer.h>
 
 #include "update_engine/common/dynamic_partition_control_stub.h"
 
@@ -87,4 +88,12 @@
   return true;
 }
 
+std::unique_ptr<android::snapshot::ISnapshotWriter>
+DynamicPartitionControlStub::OpenCowWriter(
+    const std::string& /*unsuffixed_partition_name*/,
+    const std::optional<std::string>& /*source_path*/,
+    bool /*is_append*/) {
+  return nullptr;
+}
+
 }  // namespace chromeos_update_engine