Represent speed in GCTracer functions as double instead of int.

src/heap/scavenge-job.h

Index: src/heap/scavenge-job.h
diff --git a/src/heap/scavenge-job.h b/src/heap/scavenge-job.h
index 56299a154b25d16c78a0a2186d929c9713f15ddd..fadfccdcc4ea00503b38c0b39ba3af394f65984a 100644
--- a/src/heap/scavenge-job.h
+++ b/src/heap/scavenge-job.h
@@ -47,12 +47,12 @@ class ScavengeJob {
   void NotifyIdleTask() { idle_task_pending_ = false; }
   bool IdleTaskRescheduled() { return idle_task_rescheduled_; }
 
-  static bool ReachedIdleAllocationLimit(size_t scavenge_speed_in_bytes_per_ms,
+  static bool ReachedIdleAllocationLimit(double scavenge_speed_in_bytes_per_ms,
                                          size_t new_space_size,
                                          size_t new_space_capacity);
 
   static bool EnoughIdleTimeForScavenge(double idle_time_ms,
-                                        size_t scavenge_speed_in_bytes_per_ms,
+                                        double scavenge_speed_in_bytes_per_ms,
                                         size_t new_space_size);
 
   // If we haven't recorded any scavenger events yet, we use a conservative