ART: show exact bytes along with human-friendly format

Test: Run art with -XX:DumpGCPerformanceOnShutdown on some benchmarks.
Bug: 112187497
Change-Id: I804d4aa85a1a5ed1d0b21eb934c71f73469426e9
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index 7eac3d9..8495fb5 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -341,9 +341,11 @@
     double post_gc_weighted_allocated_bytes =
         heap_->GetPostGcWeightedAllocatedBytes() / process_cpu_time;
 
-    LOG_STREAM(INFO) << "Pre GC weighted bytes allocated over CPU time: "
+    LOG_STREAM(INFO) << "Average bytes allocated at GC start, weighted by CPU time between GCs: "
+        << static_cast<uint64_t>(pre_gc_weighted_allocated_bytes)
         << " (" <<  PrettySize(pre_gc_weighted_allocated_bytes)  << ")";
-    LOG_STREAM(INFO) << "Post GC weighted bytes allocated over CPU time: "
+    LOG_STREAM(INFO) << "Average bytes allocated at GC end, weighted by CPU time between GCs: "
+        << static_cast<uint64_t>(post_gc_weighted_allocated_bytes)
         << " (" <<  PrettySize(post_gc_weighted_allocated_bytes)  << ")"
         << "\n";
   }