Avoid trusting the length encoded in the Snapshot if there is an

runtime/vm/dart.cc

Index: runtime/vm/dart.cc
===================================================================
--- runtime/vm/dart.cc	(revision 10993)
+++ runtime/vm/dart.cc	(working copy)
@@ -141,7 +141,13 @@
     // Initialize from snapshot (this should replicate the functionality
     // of Object::Init(..) in a regular isolate creation path.
     Object::InitFromSnapshot(isolate);
-    const Snapshot* snapshot = Snapshot::SetupFromBuffer(snapshot_buffer);
+    const Snapshot* snapshot =
+        Snapshot::SetupFromBuffer(snapshot_buffer, Snapshot::kTrustedLength);
+    if (snapshot == NULL) {
+      const String& message = String::Handle(String::New(
+          "Unexpected error during snapshot parsing."));
+      return ApiError::New(message);
+    }
     if (FLAG_trace_isolates) {
       OS::Print("Size of isolate snapshot = %ld\n", snapshot->length());
     }