Cache flag value to prevent performance regressions

Cache the value of the enable_per_device_input_latency_metrics flag
to prevent performace regressions.

Bug: 369812450
Test: atest inputflinger_tests
Flag: com.android.input.flags.enable_per_device_input_latency_metrics
Change-Id: I7afc2eb5ce25ae4be12bcb836f8645f1168b9e94
diff --git a/services/inputflinger/dispatcher/InputDispatcher.cpp b/services/inputflinger/dispatcher/InputDispatcher.cpp
index b0beeca..182789d 100644
--- a/services/inputflinger/dispatcher/InputDispatcher.cpp
+++ b/services/inputflinger/dispatcher/InputDispatcher.cpp
@@ -1029,7 +1029,7 @@
         const nsecs_t nextAnrCheck = processAnrsLocked();
         nextWakeupTime = std::min(nextWakeupTime, nextAnrCheck);
 
-        if (input_flags::enable_per_device_input_latency_metrics()) {
+        if (mPerDeviceInputLatencyMetricsFlag) {
             const nsecs_t nextStatisticsPush = processLatencyStatisticsLocked();
             nextWakeupTime = std::min(nextWakeupTime, nextStatisticsPush);
         }
@@ -4548,7 +4548,7 @@
             newEntry->traceTracker = mTracer->traceInboundEvent(*newEntry);
         }
 
-        if (input_flags::enable_per_device_input_latency_metrics()) {
+        if (mPerDeviceInputLatencyMetricsFlag) {
             if (args.id != android::os::IInputConstants::INVALID_INPUT_EVENT_ID &&
                 IdGenerator::getSource(args.id) == IdGenerator::Source::INPUT_READER &&
                 !mInputFilterEnabled) {