[heap,snapshot] Replace first page size from snapshots with page trimming

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 1a815eace4675735e285fafe7c47be26f24c5647..552269d2750db52402445f7eca0ddcd4008735cb 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -5462,16 +5462,19 @@ void Heap::PrintAlloctionsHash() {
 
 
 void Heap::NotifyDeserializationComplete() {
-  deserialization_complete_ = true;
-#ifdef DEBUG
-  // All pages right after bootstrapping must be marked as never-evacuate.
+  DCHECK_EQ(0, gc_count());
   PagedSpaces spaces(this);
   for (PagedSpace* s = spaces.next(); s != NULL; s = spaces.next()) {
+    if (isolate()->snapshot_available()) s->ShrinkImmortalImmovablePages();
+#ifdef DEBUG
+    // All pages right after bootstrapping must be marked as never-evacuate.
     for (Page* p : *s) {
       CHECK(p->NeverEvacuate());
     }
-  }
 #endif  // DEBUG
+  }
+
+  deserialization_complete_ = true;
 }
 
 void Heap::SetEmbedderHeapTracer(EmbedderHeapTracer* tracer) {