Add developer option for dumping GC cumulative timings on shutdown.

The option is "-XX:DumpGCPerformanceOnShutdown".
Bug: 9986416

Change-Id: If6ebb26b3e611a9dead197740dbfc64e548dc388
diff --git a/runtime/gc/heap.h b/runtime/gc/heap.h
index 9215556..30b7eb1 100644
--- a/runtime/gc/heap.h
+++ b/runtime/gc/heap.h
@@ -145,7 +145,8 @@
                 size_t max_free, double target_utilization, size_t capacity,
                 const std::string& original_image_file_name, bool concurrent_gc,
                 size_t parallel_gc_threads, size_t conc_gc_threads, bool low_memory_mode,
-                size_t long_pause_threshold, size_t long_gc_threshold, bool ignore_max_footprint);
+                size_t long_pause_threshold, size_t long_gc_threshold,
+                bool dump_gc_performance_on_shutdown, bool ignore_max_footprint);
 
   ~Heap();
 
@@ -647,6 +648,9 @@
   // If we get a GC longer than long GC log threshold, then we print out the GC after it finishes.
   const size_t long_gc_log_threshold_;
 
+  // If true, then we dump the GC cumulative timings on shutdown.
+  const bool dump_gc_performance_on_shutdown_;
+
   // If we ignore the max footprint it lets the heap grow until it hits the heap capacity, this is
   // useful for benchmarking since it reduces time spent in GC to a low %.
   const bool ignore_max_footprint_;