Extract non-IO part of mksnapshot into an API method.

src/snapshot-external.cc

 // 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.
 
 // Used for building with external snapshots.
 
 #include "src/snapshot.h"
 
 #include "src/serialize.h"
 #include "src/snapshot-source-sink.h"
 #include "src/v8.h"  // for V8::Initialize
 
 
 #ifndef V8_USE_EXTERNAL_STARTUP_DATA
 #error snapshot-external.cc is used only for the external snapshot build.
 #endif  // V8_USE_EXTERNAL_STARTUP_DATA
 
 
 namespace v8 {
 namespace internal {
 
 static v8::StartupData external_startup_blob = {NULL, 0};
 
 void SetSnapshotFromFile(StartupData* snapshot_blob) {
   DCHECK(snapshot_blob);
   DCHECK(snapshot_blob->data);
   DCHECK(snapshot_blob->raw_size > 0);
   DCHECK(!external_startup_blob.data);
+  // Validate snapshot blob.
+  DCHECK(!Snapshot::ExtractStartupData(snapshot_blob).is_empty());
+  DCHECK(!Snapshot::ExtractContextData(snapshot_blob).is_empty());
   external_startup_blob = *snapshot_blob;
-
-  // Validate snapshot blob.
-  DCHECK(!Snapshot::StartupSnapshot().is_empty());
-  DCHECK(!Snapshot::ContextSnapshot().is_empty());
 }
 
 
 const v8::StartupData Snapshot::SnapshotBlob() { return external_startup_blob; }
 } }  // namespace v8::internal