Use conservative heap growing factor for background tab.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 54dfc7ae1a26da7fb32d5f3922da73012a72102a..750827968dcd757edff47ece2ed0948930aa688f 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1806,6 +1806,10 @@ class Heap {
   // last GC.
   bool old_gen_exhausted_;
 
+  // Indicates that memory usage is more important than latency.
+  // TODO(ulan): Merge it with memory reducer once chromium:490559 is fixed.
+  bool optimize_for_memory_usage_;
+
   // Indicates that inline bump-pointer allocation has been globally disabled
   // for all spaces. This is used to disable allocations in generated code.
   bool inline_allocation_disabled_;