Store embed-script flag as metadata into snapshot blob.

src/snapshot-common.cc

Index: src/snapshot-common.cc
diff --git a/src/snapshot-common.cc b/src/snapshot-common.cc
index 09cf7223ffc931f8e889c524e7aebd965ad1b11d..c2ce60d5fbdbe220eb21e7578636a1eb936a7ffc 100644
--- a/src/snapshot-common.cc
+++ b/src/snapshot-common.cc
@@ -19,6 +19,21 @@ bool Snapshot::HaveASnapshotToStartFrom() {
 }
 
 
+#ifdef DEBUG
+bool Snapshot::SnapshotIsValid(v8::StartupData* snapshot_blob) {
+  return !Snapshot::ExtractStartupData(snapshot_blob).is_empty() &&
+         !Snapshot::ExtractContextData(snapshot_blob).is_empty();
+}
+#endif  // DEBUG
+
+
+bool Snapshot::EmbedsScript() {
+  if (!HaveASnapshotToStartFrom()) return false;
+  const v8::StartupData blob = SnapshotBlob();
+  return ExtractMetadata(&blob).embeds_script();
+}
+
+
 bool Snapshot::Initialize(Isolate* isolate) {
   if (!HaveASnapshotToStartFrom()) return false;
   base::ElapsedTimer timer;
@@ -54,6 +69,9 @@ MaybeHandle<Context> Snapshot::NewContextFromSnapshot(
   Handle<Object> result;
   if (!maybe_context.ToHandle(&result)) return MaybeHandle<Context>();
   CHECK(result->IsContext());
+  // If the snapshot does not contain a custom script, we need to update
+  // the global object for exactly one context.
+  CHECK(EmbedsScript() || (*outdated_contexts_out)->length() == 1);
   if (FLAG_profile_deserialization) {
     double ms = timer.Elapsed().InMillisecondsF();
     int bytes = context_data.length();
@@ -65,28 +83,37 @@ MaybeHandle<Context> Snapshot::NewContextFromSnapshot(
 
 v8::StartupData Snapshot::CreateSnapshotBlob(
     const Vector<const byte> startup_data,
-    const Vector<const byte> context_data) {
+    const Vector<const byte> context_data, Snapshot::Metadata metadata) {
   int startup_length = startup_data.length();
   int context_length = context_data.length();
-  int context_offset = kIntSize + startup_length;
+  int context_offset = ContextOffset(startup_length);
+
   int length = context_offset + context_length;
   char* data = new char[length];
 
-  memcpy(data, &startup_length, kIntSize);
-  memcpy(data + kIntSize, startup_data.begin(), startup_length);
+  memcpy(data + kMetadataOffset, &metadata.RawValue(), kInt32Size);
+  memcpy(data + kStartupLengthOffset, &startup_length, kInt32Size);
+  memcpy(data + kStartupDataOffset, startup_data.begin(), startup_length);
   memcpy(data + context_offset, context_data.begin(), context_length);
   v8::StartupData result = {data, length};
   return result;
 }
 
 
+Snapshot::Metadata Snapshot::ExtractMetadata(const v8::StartupData* data) {
+  uint32_t raw;
+  memcpy(&raw, data->data + kMetadataOffset, kInt32Size);
+  return Metadata(raw);
+}
+
+
 Vector<const byte> Snapshot::ExtractStartupData(const v8::StartupData* data) {
   DCHECK_LT(kIntSize, data->raw_size);
   int startup_length;
-  memcpy(&startup_length, data->data, kIntSize);
+  memcpy(&startup_length, data->data + kStartupLengthOffset, kInt32Size);
   DCHECK_LT(startup_length, data->raw_size);
   const byte* startup_data =
-      reinterpret_cast<const byte*>(data->data + kIntSize);
+      reinterpret_cast<const byte*>(data->data + kStartupDataOffset);
   return Vector<const byte>(startup_data, startup_length);
 }
 
@@ -94,8 +121,8 @@ Vector<const byte> Snapshot::ExtractStartupData(const v8::StartupData* data) {
 Vector<const byte> Snapshot::ExtractContextData(const v8::StartupData* data) {
   DCHECK_LT(kIntSize, data->raw_size);
   int startup_length;
-  memcpy(&startup_length, data->data, kIntSize);
-  int context_offset = kIntSize + startup_length;
+  memcpy(&startup_length, data->data + kStartupLengthOffset, kIntSize);
+  int context_offset = ContextOffset(startup_length);
   const byte* context_data =
       reinterpret_cast<const byte*>(data->data + context_offset);
   DCHECK_LT(context_offset, data->raw_size);