Introduce a flag to change the new space growth factor

A useful value would be 4, so we get 1, 4, 16MB (instead of the default
value 2 which leads to 1, 2, 4, 8, 16)

BUG=none
R=hpayer@chromium.org
LOG=n

Review URL: https://codereview.chromium.org/753513002

Cr-Commit-Position: refs/heads/master@{#25462}

src/flag-definitions.h

@@ -530,6 +530,7 @@ DEFINE_INT(target_semi_space_size, 0,
 DEFINE_INT(max_semi_space_size, 0,
            "max size of a semi-space (in MBytes), the new space consists of two"
            "semi-spaces")
+DEFINE_INT(semi_space_growth_factor, 2, "factor by which to grow the new space")
 DEFINE_INT(max_old_space_size, 0, "max size of the old space (in Mbytes)")
 DEFINE_INT(max_executable_size, 0, "max size of executable memory (in Mbytes)")
 DEFINE_BOOL(gc_global, false, "always perform global GCs")

src/heap/heap.cc

@@ -5059,6 +5059,10 @@ bool Heap::ConfigureHeap(int max_semi_space_size, int max_old_space_size,
 
   target_semispace_size_ = Max(initial_semispace_size_, target_semispace_size_);
 
+  if (FLAG_semi_space_growth_factor < 2) {
+    FLAG_semi_space_growth_factor = 2;
+  }
+
   // The old generation is paged and needs at least one page for each space.
   int paged_space_count = LAST_PAGED_SPACE - FIRST_PAGED_SPACE + 1;
   max_old_generation_size_ =

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)) {