[snapshot] Hide private parts of snapshot.h

snapshot.h is intended to be the public header for the snapshot
component, and not the right place for private declarations. This moves
them into a new SnapshotImpl class in snapshot.cc (previously named
snapshot-common.cc).

Bug: v8:10416
Change-Id: If34ad8d6e189050686942488fb8e99c3d310beee
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2144062
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67279}

BUILD.gn

@@ -2960,13 +2960,13 @@ v8_source_set("v8_base_without_compiler") {
     "src/snapshot/serializer-common.h",
     "src/snapshot/serializer.cc",
     "src/snapshot/serializer.h",
-    "src/snapshot/snapshot-common.cc",
     "src/snapshot/snapshot-compression.cc",
     "src/snapshot/snapshot-compression.h",
     "src/snapshot/snapshot-data.cc",
     "src/snapshot/snapshot-data.h",
     "src/snapshot/snapshot-source-sink.cc",
     "src/snapshot/snapshot-source-sink.h",
+    "src/snapshot/snapshot.cc",
     "src/snapshot/snapshot.h",
     "src/snapshot/startup-deserializer.cc",
     "src/snapshot/startup-deserializer.h",

src/snapshot/snapshot.h

-// Copyright 2006-2008 the V8 project authors. All rights reserved.
+// Copyright 2020 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 "include/v8.h"
-
-#include "src/base/memory.h"
-#include "src/utils/vector.h"
+#include "include/v8.h"  // For StartupData.
+#include "src/common/globals.h"
 
 namespace v8 {
 namespace internal {
@@ -19,7 +17,15 @@ class JSGlobalProxy;
 
 class Snapshot : public AllStatic {
  public:
-  // ---------------- Deserialization ----------------
+  // ---------------- Serialization -------------------------------------------
+
+  static v8::StartupData CreateSnapshotBlob(
+      const SnapshotData* startup_snapshot_in,
+      const SnapshotData* read_only_snapshot_in,
+      const std::vector<SnapshotData*>& context_snapshots_in,
+      bool can_be_rehashed);
+
+  // ---------------- Deserialization -----------------------------------------
 
   // Initialize the Isolate from the internal snapshot. Returns false if no
   // snapshot could be found.
@@ -31,95 +37,19 @@ class Snapshot : public AllStatic {
       size_t context_index,
       v8::DeserializeEmbedderFieldsCallback embedder_fields_deserializer);
 
-  // ---------------- Helper methods ----------------
+  // ---------------- Helper methods ------------------------------------------
 
   static bool HasContextSnapshot(Isolate* isolate, size_t index);
   static bool EmbedsScript(Isolate* isolate);
+  V8_EXPORT_PRIVATE static bool VerifyChecksum(const v8::StartupData* data);
+  static bool ExtractRehashability(const v8::StartupData* data);
 
   // To be implemented by the snapshot source.
   static const v8::StartupData* DefaultSnapshotBlob();
 
-  V8_EXPORT_PRIVATE static bool VerifyChecksum(const v8::StartupData* data);
-
-  // ---------------- Serialization ----------------
-
-  static v8::StartupData CreateSnapshotBlob(
-      const SnapshotData* startup_snapshot_in,
-      const SnapshotData* read_only_snapshot_in,
-      const std::vector<SnapshotData*>& context_snapshots_in,
-      bool can_be_rehashed);
-
 #ifdef DEBUG
   static bool SnapshotIsValid(const v8::StartupData* snapshot_blob);
 #endif  // DEBUG
-
-  static bool ExtractRehashability(const v8::StartupData* data);
-
- private:
-  static uint32_t ExtractNumContexts(const v8::StartupData* data);
-  static uint32_t ExtractContextOffset(const v8::StartupData* data,
-                                       uint32_t index);
-  static Vector<const byte> ExtractStartupData(const v8::StartupData* data);
-  static Vector<const byte> ExtractReadOnlyData(const v8::StartupData* data);
-  static Vector<const byte> ExtractContextData(const v8::StartupData* data,
-                                               uint32_t index);
-
-  static uint32_t GetHeaderValue(const v8::StartupData* data, uint32_t offset) {
-    return base::ReadLittleEndianValue<uint32_t>(
-        reinterpret_cast<Address>(data->data) + offset);
-  }
-  static void SetHeaderValue(char* data, uint32_t offset, uint32_t value) {
-    base::WriteLittleEndianValue(reinterpret_cast<Address>(data) + offset,
-                                 value);
-  }
-
-  static void CheckVersion(const v8::StartupData* data);
-
-  // Snapshot blob layout:
-  // [0] number of contexts N
-  // [1] rehashability
-  // [2] checksum
-  // [3] (128 bytes) version string
-  // [4] offset to readonly
-  // [5] offset to context 0
-  // [6] offset to context 1
-  // ...
-  // ... offset to context N - 1
-  // ... startup snapshot data
-  // ... read-only snapshot data
-  // ... context 0 snapshot data
-  // ... context 1 snapshot data
-
-  static const uint32_t kNumberOfContextsOffset = 0;
-  // TODO(yangguo): generalize rehashing, and remove this flag.
-  static const uint32_t kRehashabilityOffset =
-      kNumberOfContextsOffset + kUInt32Size;
-  static const uint32_t kChecksumOffset = kRehashabilityOffset + kUInt32Size;
-  static const uint32_t kVersionStringOffset = kChecksumOffset + kUInt32Size;
-  static const uint32_t kVersionStringLength = 64;
-  static const uint32_t kReadOnlyOffsetOffset =
-      kVersionStringOffset + kVersionStringLength;
-  static const uint32_t kFirstContextOffsetOffset =
-      kReadOnlyOffsetOffset + kUInt32Size;
-
-  static Vector<const byte> ChecksummedContent(const v8::StartupData* data) {
-    STATIC_ASSERT(kVersionStringOffset == kChecksumOffset + kUInt32Size);
-    const uint32_t kChecksumStart = kVersionStringOffset;
-    return Vector<const byte>(
-        reinterpret_cast<const byte*>(data->data + kChecksumStart),
-        data->raw_size - kChecksumStart);
-  }
-
-  static uint32_t StartupSnapshotOffset(int num_contexts) {
-    return POINTER_SIZE_ALIGN(kFirstContextOffsetOffset +
-                              num_contexts * kInt32Size);
-  }
-
-  static uint32_t ContextSnapshotOffsetOffset(int index) {
-    return kFirstContextOffsetOffset + index * kInt32Size;
-  }
-
-  DISALLOW_IMPLICIT_CONSTRUCTORS(Snapshot);
 };
 
 // Convenience wrapper around snapshot data blob creation used e.g. by tests and