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/LatencyAggregator.h b/services/inputflinger/dispatcher/LatencyAggregator.h
index accfc29..60b6813 100644
--- a/services/inputflinger/dispatcher/LatencyAggregator.h
+++ b/services/inputflinger/dispatcher/LatencyAggregator.h
@@ -56,7 +56,7 @@
      */
     void processTimeline(const InputEventTimeline& timeline) override;
 
-    std::string dump(const char* prefix);
+    std::string dump(const char* prefix) const;
 
     ~LatencyAggregator();