Add const annotations to dispatcher

These allow us to dump the dispatcher state from other const dispatcher
methods.

Bug: 274073185
Test: m
Change-Id: I483d957b243bca595c147656d8305fdc4f43fb33
diff --git a/services/inputflinger/dispatcher/LatencyTracker.h b/services/inputflinger/dispatcher/LatencyTracker.h
index 64dfeef..4212da8 100644
--- a/services/inputflinger/dispatcher/LatencyTracker.h
+++ b/services/inputflinger/dispatcher/LatencyTracker.h
@@ -55,7 +55,7 @@
     void trackGraphicsLatency(int32_t inputEventId, const sp<IBinder>& connectionToken,
                               std::array<nsecs_t, GraphicsTimeline::SIZE> timeline);
 
-    std::string dump(const char* prefix);
+    std::string dump(const char* prefix) const;
 
 private:
     /**