Only skip operation on snapshot partitions

On Virtual A/B devices, don't skip SOURCE_COPY on
static partitions.

Test: update_engine_unittest
Test: incremental update to self
Change-Id: I5c93b501e09f50f559151eb77d83052373c90d0d
diff --git a/mock_dynamic_partition_control.h b/mock_dynamic_partition_control.h
index db8e834..09b825d 100644
--- a/mock_dynamic_partition_control.h
+++ b/mock_dynamic_partition_control.h
@@ -17,6 +17,7 @@
 #include <stdint.h>
 
 #include <memory>
+#include <set>
 #include <string>
 
 #include <gmock/gmock.h>
@@ -69,6 +70,10 @@
   MOCK_METHOD1(GetSuperPartitionName, std::string(uint32_t));
   MOCK_METHOD0(GetVirtualAbFeatureFlag, FeatureFlag());
   MOCK_METHOD0(FinishUpdate, bool());
+
+  void set_fake_mapped_devices(const std::set<std::string>& fake) override {
+    DynamicPartitionControlAndroid::set_fake_mapped_devices(fake);
+  }
 };
 
 }  // namespace chromeos_update_engine