Add a flag to specify fixed heap growing factor to be used in tests.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 923f434ed019969a61ba765537be4fa72b0819e9..cddd0353c888ff2c1298599dc6317706b82f5a5c 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -4916,6 +4916,10 @@ void Heap::SetOldGenerationAllocationLimit(intptr_t old_gen_size,
     factor = kMinHeapGrowingFactor;
   }
 
+  if (FLAG_heap_growing_percent > 0) {
+    factor = 1.0 + FLAG_heap_growing_percent / 100.0;
+  }
+
   old_generation_allocation_limit_ =
       CalculateOldGenerationAllocationLimit(factor, old_gen_size);