Add parallel recompilation time to histogram and plot execution pause times.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 307960b737564e495b508be5cc33b70ae9f9c8f5..32c2fe4f0964d89b1ef5c1bf698b8d7b4e52be01 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -644,13 +644,13 @@ bool Heap::CollectGarbage(AllocationSpace space,
     // Tell the tracer which collector we've selected.
     tracer.set_collector(collector);
 
-    HistogramTimer* rate = (collector == SCAVENGER)
-        ? isolate_->counters()->gc_scavenger()
-        : isolate_->counters()->gc_compactor();
-    rate->Start();
-    next_gc_likely_to_collect_more =
-        PerformGarbageCollection(collector, &tracer);
-    rate->Stop();
+    {
+      HistogramTimerScope histogram_timer_scope(
+          (collector == SCAVENGER) ? isolate_->counters()->gc_scavenger()
+                                   : isolate_->counters()->gc_compactor());
+      next_gc_likely_to_collect_more =
+          PerformGarbageCollection(collector, &tracer);
+    }
 
     ASSERT(collector == SCAVENGER || incremental_marking()->IsStopped());