Move Stopwatch into its own header

Bug: 29748723
Test: netd_integration_test

(cherry picked from commit cc544162e08dd0df271cd77a3f2c85dbaaa461e2)

Change-Id: I02a9ad8591d1c98f146fe2fe8c3b25a2d752ab55
diff --git a/server/SockDiag.cpp b/server/SockDiag.cpp
index f6b8b10..d5150e2 100644
--- a/server/SockDiag.cpp
+++ b/server/SockDiag.cpp
@@ -35,6 +35,7 @@
 #include "NetdConstants.h"
 #include "Permission.h"
 #include "SockDiag.h"
+#include "Stopwatch.h"
 
 #include <chrono>