Let store buffer start out small for a 1Mbyte saving in boot

src/heap.cc

Index: src/heap.cc
===================================================================
--- src/heap.cc	(revision 10131)
+++ src/heap.cc	(working copy)
@@ -1012,7 +1012,7 @@
       // Store Buffer overflowed while scanning promoted objects.  These are not
       // in any particular page, though they are likely to be clustered by the
       // allocation routines.
-      store_buffer_->HandleFullness();
+      store_buffer_->EnsureSpace(StoreBuffer::kStoreBufferSize);
     } else {
       // Store Buffer overflowed while scanning a particular old space page for
       // pointers to new space.