Fix external-snapshot startup when snapshot is missing, but natives source is available

src/isolate.h

Index: src/isolate.h
diff --git a/src/isolate.h b/src/isolate.h
index 80c3daea746f6c6704c88ef58386cd469b4dacc8..e8576f5940d599b30617984b46342c1cffbc1dc7 100644
--- a/src/isolate.h
+++ b/src/isolate.h
@@ -986,7 +986,9 @@ class Isolate {
   }
 
   bool serializer_enabled() const { return serializer_enabled_; }
-  bool snapshot_available() const { return snapshot_blob_ != NULL; }
+  bool snapshot_available() const {
+    return snapshot_blob_ != NULL && snapshot_blob_->raw_size != 0;

[vogelheim, 2015/04/01 17:02:13]

When does this happen?

I'm a bit surprised. I don't think an embedder should give us an empty snapshot;
they should just not give us a snapshot at all. In the static initialization
case we at least DCHECK for this situation.

ref:
https://code.google.com/p/chromium/codesearch#chromium/src/v8/src/snapshot/sn...

[Erik Corry, 2015/04/01 17:07:29]

This isn't the embedder giving us an empty snapshot, it's our own default
snapshot, which has a null data field.

[vogelheim, 2015/04/01 17:21:09]

Oh. :-(

I guess it shouldn't do that; but since it does we'll need the check.

+  }
 
   bool IsDead() { return has_fatal_error_; }
   void SignalFatalError() { has_fatal_error_ = true; }