Add input flag enable_per_device_input_latency_metrics

Bug: 270049345
Test: presubmit
Flag: EXEMPT creating flag
Change-Id: I95d6dd8c2ce47f6fd02acd8b44c9b000382c71df
diff --git a/libs/input/input_flags.aconfig b/libs/input/input_flags.aconfig
index ab117b8..8e91f11 100644
--- a/libs/input/input_flags.aconfig
+++ b/libs/input/input_flags.aconfig
@@ -171,3 +171,10 @@
   description: "Include AXIS_RELATIVE_X and AXIS_RELATIVE_Y values when reporting touches from captured touchpads."
   bug: "330522990"
 }
+
+flag {
+  name: "enable_per_device_input_latency_metrics"
+  namespace: "input"
+  description: "Capture input latency metrics on a per device granular level using histograms."
+  bug: "270049345"
+}