Make new space allocation throughput estimation more accurate.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 4535bbb2cb08b4139e10b6a83cf97c92b2c57332..8b41fb7b2647295544c9eb1cf766b36972bbe979 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1312,6 +1312,19 @@ class Heap {
     }
   }
 
+  void UpdateNewSpaceAllocationCounter() {
+    new_space_allocation_counter_ = NewSpaceAllocationCounter();
+  }
+
+  size_t NewSpaceAllocationCounter() {
+    return new_space_allocation_counter_ + new_space()->AllocatedSinceLastGC();
+  }
+
+  // This should be used only for testing.
+  void set_new_space_allocation_counter(size_t new_value) {
+    new_space_allocation_counter_ = new_value;
+  }
+
   // Update GC statistics that are tracked on the Heap.
   void UpdateCumulativeGCStatistics(double duration, double spent_in_mutator,
                                     double marking_time);
@@ -2182,6 +2195,11 @@ class Heap {
   size_t full_codegen_bytes_generated_;
   size_t crankshaft_codegen_bytes_generated_;
 
+  // This counter is increased before each GC and never reset.
+  // To account for the bytes allocated since the last GC, use the
+  // NewSpaceAllocationCounter() function.
+  size_t new_space_allocation_counter_;
+
   // If the --deopt_every_n_garbage_collections flag is set to a positive value,
   // this variable holds the number of garbage collections since the last
   // deoptimization triggered by garbage collection.