Make snapshot.h usable without objects-inl.h header.

src/snapshot/snapshot-common.cc

Index: src/snapshot/snapshot-common.cc
diff --git a/src/snapshot/snapshot-common.cc b/src/snapshot/snapshot-common.cc
index 5a849f63b49f6407c9ac4b63a4de4f09a2be3e21..0b7e11d1ec4a0f225e88d9d5a2bce331ad2cb222 100644
--- a/src/snapshot/snapshot-common.cc
+++ b/src/snapshot/snapshot-common.cc
@@ -21,6 +21,13 @@ bool Snapshot::SnapshotIsValid(v8::StartupData* snapshot_blob) {
 #endif  // DEBUG
 
 
+bool Snapshot::HaveASnapshotToStartFrom(Isolate* isolate) {
+  // Do not use snapshots if the isolate is used to create snapshots.
+  return isolate->snapshot_blob() != NULL &&
+         isolate->snapshot_blob()->data != NULL;
+}
+
+
 bool Snapshot::EmbedsScript(Isolate* isolate) {
   if (!isolate->snapshot_available()) return false;
   return ExtractMetadata(isolate->snapshot_blob()).embeds_script();