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

src/snapshot/snapshot.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_SNAPSHOT_SNAPSHOT_H_
 #define V8_SNAPSHOT_SNAPSHOT_H_
 
 #include "src/snapshot/partial-serializer.h"
 #include "src/snapshot/startup-serializer.h"
 
@@ skipping 49 matching lines @@
   static MaybeHandle<Context> NewContextFromSnapshot(
       Isolate* isolate, Handle<JSGlobalProxy> global_proxy,
       size_t context_index);
 
   static bool HaveASnapshotToStartFrom(Isolate* isolate);
 
   static bool HasContextSnapshot(Isolate* isolate, size_t index);
 
   static bool EmbedsScript(Isolate* isolate);
 
-  static uint32_t SizeOfFirstPage(Isolate* isolate, AllocationSpace space);
-
-
   // To be implemented by the snapshot source.
   static const v8::StartupData* DefaultSnapshotBlob();
 
   static v8::StartupData CreateSnapshotBlob(
       const SnapshotData* startup_snapshot,
       const List<SnapshotData*>* context_snapshots);
 
 #ifdef DEBUG
   static bool SnapshotIsValid(v8::StartupData* snapshot_blob);
 #endif  // DEBUG
 
  private:
   static int ExtractNumContexts(const v8::StartupData* data);
   static Vector<const byte> ExtractStartupData(const v8::StartupData* data);
   static Vector<const byte> ExtractContextData(const v8::StartupData* data,
                                                int index);
 
   // Snapshot blob layout:
-  // [0 - 5] pre-calculated first page sizes for paged spaces
-  // [6] number of contexts N
-  // [7] offset to context 0
-  // [8] offset to context 1
+  // [0] number of contexts N
+  // [1] offset to context 0
+  // [2] offset to context 1
   // ...
   // ... offset to context N - 1
   // ... startup snapshot data
   // ... context 0 snapshot data
   // ... context 1 snapshot data
 
-  static const int kNumPagedSpaces = LAST_PAGED_SPACE - FIRST_PAGED_SPACE + 1;
-
-  static const int kFirstPageSizesOffset = 0;
-  static const int kNumberOfContextsOffset =
-      kFirstPageSizesOffset + kNumPagedSpaces * kInt32Size;
+  static const int kNumberOfContextsOffset = 0;
   static const int kFirstContextOffsetOffset =
       kNumberOfContextsOffset + kInt32Size;
 
   static int StartupSnapshotOffset(int num_contexts) {
     return kFirstContextOffsetOffset + num_contexts * kInt32Size;
   }
 
   static int ContextSnapshotOffsetOffset(int index) {
     return kFirstContextOffsetOffset + index * kInt32Size;
   }
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(Snapshot);
 };
 
 #ifdef V8_USE_EXTERNAL_STARTUP_DATA
 void SetSnapshotFromFile(StartupData* snapshot_blob);
 #endif
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_SNAPSHOT_SNAPSHOT_H_