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

src/heap/spaces.h

Index: src/heap/spaces.h
diff --git a/src/heap/spaces.h b/src/heap/spaces.h
index d024c4b6a3000e700e7bda19313c92024c764a6c..747055db7bc5ccb64f24a7236996be2df881d13c 100644
--- a/src/heap/spaces.h
+++ b/src/heap/spaces.h
@@ -817,6 +817,8 @@ class Page : public MemoryChunk {
     available_in_free_list_.Increment(available);
   }
 
+  size_t ShrinkToHighWaterMark();
+
 #ifdef DEBUG
   void Print();
 #endif  // DEBUG
@@ -1305,6 +1307,8 @@ class MemoryAllocator {
                              intptr_t commit_area_size,
                              Executability executable, Space* space);
 
+  void ShrinkChunk(MemoryChunk* chunk, size_t bytes_to_shrink);
+
   Address ReserveAlignedMemory(size_t requested, size_t alignment,
                                base::VirtualMemory* controller);
   Address AllocateAlignedMemory(size_t reserve_size, size_t commit_size,
@@ -2186,6 +2190,10 @@ class PagedSpace : public Space {
   iterator begin() { return iterator(anchor_.next_page()); }
   iterator end() { return iterator(&anchor_); }
 
+  // Shrink immortal immovable pages of the space to be exactly the size needed
+  // using the high water mark.
+  void ShrinkImmortalImmovablePages();
+
  protected:
   // PagedSpaces that should be included in snapshots have different, i.e.,
   // smaller, initial pages.