SF: Move frontend code to frontend namespace

Fixes: b/259553365
Test: presubmit
Change-Id: I47338ec3e8d151e09b3c22c0544ba948dc25b98d
diff --git a/services/surfaceflinger/FrontEnd/TransactionHandler.h b/services/surfaceflinger/FrontEnd/TransactionHandler.h
index 2b6f07d..a06b870 100644
--- a/services/surfaceflinger/FrontEnd/TransactionHandler.h
+++ b/services/surfaceflinger/FrontEnd/TransactionHandler.h
@@ -18,9 +18,6 @@
 
 #include <semaphore.h>
 #include <cstdint>
-#include <mutex>
-#include <queue>
-#include <thread>
 #include <vector>
 
 #include <LocklessQueue.h>
@@ -30,6 +27,10 @@
 #include <ftl/small_vector.h>
 
 namespace android {
+
+class TestableSurfaceFlinger;
+namespace surfaceflinger::frontend {
+
 class TransactionHandler {
 public:
     struct TransactionFlushState {
@@ -60,7 +61,7 @@
 
 private:
     // For unit tests
-    friend class TestableSurfaceFlinger;
+    friend class ::android::TestableSurfaceFlinger;
 
     int flushPendingTransactionQueues(std::vector<TransactionState>&, TransactionFlushState&);
     TransactionReadiness applyFilters(TransactionFlushState&);
@@ -71,5 +72,5 @@
     ftl::SmallVector<TransactionFilter, 2> mTransactionReadyFilters;
     std::vector<uint64_t> mStalledTransactions;
 };
-
+} // namespace surfaceflinger::frontend
 } // namespace android