Represent speed in GCTracer functions as double instead of int.

test/unittests/heap/scavenge-job-unittest.cc

Index: test/unittests/heap/scavenge-job-unittest.cc
diff --git a/test/unittests/heap/scavenge-job-unittest.cc b/test/unittests/heap/scavenge-job-unittest.cc
index dbd463c2d568536e51fa4089c798892a7d301845..91abbb1f8fbe05bdb25fdce40305c898b29dc51f 100644
--- a/test/unittests/heap/scavenge-job-unittest.cc
+++ b/test/unittests/heap/scavenge-job-unittest.cc
@@ -71,7 +71,7 @@ TEST(ScavengeJob, AllocationLimitHighScavengeSpeed) {
   EXPECT_FALSE(ScavengeJob::ReachedIdleAllocationLimit(
       scavenge_speed, expected_size - 1, kNewSpaceCapacity));
   EXPECT_TRUE(ScavengeJob::ReachedIdleAllocationLimit(
-      scavenge_speed, expected_size, kNewSpaceCapacity));
+      scavenge_speed, expected_size + 1, kNewSpaceCapacity));
 }