Make new space allocation throughput estimation more accurate.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 2ba75d0f27c6b40eeaec90ca3c2e25c2f0a95cb1..b9ead9bfddc33befbb502d016aa3b5c8e88ddabf 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -140,6 +140,7 @@ Heap::Heap()
       gc_count_at_last_idle_gc_(0),
       full_codegen_bytes_generated_(0),
       crankshaft_codegen_bytes_generated_(0),
+      new_space_allocation_counter_(0),
       gcs_since_last_deopt_(0),
       allocation_sites_scratchpad_length_(0),
       promotion_queue_(this),
@@ -460,6 +461,7 @@ void Heap::GarbageCollectionPrologue() {
     maximum_size_scavenges_ = 0;
   }
   CheckNewSpaceExpansionCriteria();
+  UpdateNewSpaceAllocationCounter();
 }
 
 
@@ -4631,6 +4633,7 @@ bool Heap::IdleNotification(double deadline_in_seconds) {
   intptr_t limit = old_generation_allocation_limit_;
   if (is_long_idle_notification) {
     limit = idle_old_generation_allocation_limit_;
+    tracer()->SampleNewSpaceAllocation(start_ms, NewSpaceAllocationCounter());
   }
 
   heap_state.can_start_incremental_marking =
@@ -4653,8 +4656,7 @@ bool Heap::IdleNotification(double deadline_in_seconds) {
   heap_state.used_new_space_size = new_space_.Size();
   heap_state.new_space_capacity = new_space_.Capacity();
   heap_state.new_space_allocation_throughput_in_bytes_per_ms =
-      static_cast<size_t>(
-          tracer()->NewSpaceAllocationThroughputInBytesPerMillisecond());
+      tracer()->NewSpaceAllocationThroughputInBytesPerMillisecond();
 
   GCIdleTimeAction action =
       gc_idle_time_handler_.Compute(idle_time_in_ms, heap_state);