Introduce a flag to change the new space growth factor

src/heap/spaces.cc

Index: src/heap/spaces.cc
diff --git a/src/heap/spaces.cc b/src/heap/spaces.cc
index 51a0ef68e0fb72b18d671e20fddc57451f81b805..554b71706df22cb2255809cd2293b56a7ab31848 100644
--- a/src/heap/spaces.cc
+++ b/src/heap/spaces.cc
@@ -1313,7 +1313,8 @@ void NewSpace::Grow() {
   // Double the semispace size but only up to maximum capacity.
   DCHECK(TotalCapacity() < MaximumCapacity());
   int new_capacity =
-      Min(MaximumCapacity(), 2 * static_cast<int>(TotalCapacity()));
+      Min(MaximumCapacity(),
+          FLAG_semi_space_growth_factor * static_cast<int>(TotalCapacity()));
   if (to_space_.GrowTo(new_capacity)) {
     // Only grow from space if we managed to grow to-space.
     if (!from_space_.GrowTo(new_capacity)) {