Consolidate WpHash declaration to a common file

Bug: b/193932763
Test: frameworks/native/test
Change-Id: Ib19f191ed8031b77c059b644fe5df3c8137e6619
diff --git a/services/surfaceflinger/FpsReporter.h b/services/surfaceflinger/FpsReporter.h
index bd7b9a5..438b1aa 100644
--- a/services/surfaceflinger/FpsReporter.h
+++ b/services/surfaceflinger/FpsReporter.h
@@ -24,6 +24,7 @@
 
 #include "Clock.h"
 #include "FrameTimeline/FrameTimeline.h"
+#include "WpHash.h"
 
 namespace android {
 
@@ -50,11 +51,6 @@
 
 private:
     mutable std::mutex mMutex;
-    struct WpHash {
-        size_t operator()(const wp<IBinder>& p) const {
-            return std::hash<IBinder*>()(p.unsafe_get());
-        }
-    };
 
     struct TrackedListener {
         sp<gui::IFpsListener> listener;