[adb] Don't copy features set on each get()
The features are already cached in a static and don't change.
Let's return the cached set instead of copying it every time.
Bug: 150183149
Test: manual
Change-Id: Ifdca852cc3b32e09e50ea4771f7878987c46cce8
diff --git a/adb/transport.h b/adb/transport.h
index 4b2e000..e93c31c 100644
--- a/adb/transport.h
+++ b/adb/transport.h
@@ -30,7 +30,7 @@
#include <string>
#include <string_view>
#include <thread>
-#include <unordered_set>
+#include <vector>
#include <android-base/macros.h>
#include <android-base/thread_annotations.h>
@@ -40,7 +40,10 @@
#include "adb_unique_fd.h"
#include "types.h"
-typedef std::unordered_set<std::string> FeatureSet;
+// Even though the feature set is used as a set, we only have a dozen or two
+// of available features at any moment. Vector works much better in terms of
+// both memory usage and performance for these sizes.
+using FeatureSet = std::vector<std::string>;
namespace adb {
namespace tls {