SF: Move frontend code to frontend namespace

Fixes: b/259553365
Test: presubmit
Change-Id: I47338ec3e8d151e09b3c22c0544ba948dc25b98d
diff --git a/services/surfaceflinger/tests/unittests/TransactionApplicationTest.cpp b/services/surfaceflinger/tests/unittests/TransactionApplicationTest.cpp
index 488d4a9..d84698f 100644
--- a/services/surfaceflinger/tests/unittests/TransactionApplicationTest.cpp
+++ b/services/surfaceflinger/tests/unittests/TransactionApplicationTest.cpp
@@ -42,6 +42,8 @@
 using testing::Return;
 
 using FakeHwcDisplayInjector = TestableSurfaceFlinger::FakeHwcDisplayInjector;
+using frontend::TransactionHandler;
+
 constexpr nsecs_t TRANSACTION_TIMEOUT = s2ns(5);
 class TransactionApplicationTest : public testing::Test {
 public: