Compute the heap growing factor based on mutator utilization and allocation throughput.

src/heap/gc-tracer.h

Index: src/heap/gc-tracer.h
diff --git a/src/heap/gc-tracer.h b/src/heap/gc-tracer.h
index 33a2ab8cacccb4b4d0e19ef3408f302b63cca330..9a7b28d4fb5624481b1b283c9d5332715d18f323 100644
--- a/src/heap/gc-tracer.h
+++ b/src/heap/gc-tracer.h
@@ -402,10 +402,10 @@ class GCTracer {
   // Returns 0 if no allocation events have been recorded.
   size_t AllocationThroughputInBytesPerMillisecond(double time_ms) const;
 
-  // Allocation throughput in heap in bytes/milliseconds in
+  // Allocation throughput in old generation in bytes/milliseconds in
   // the last five seconds.
   // Returns 0 if no allocation events have been recorded.
-  size_t CurrentAllocationThroughputInBytesPerMillisecond() const;
+  size_t CurrentOldGenerationAllocationThroughputInBytesPerMillisecond() const;
 
   // Computes the context disposal rate in milliseconds. It takes the time
   // frame of the first recorded context disposal to the current time and