Fix background compilation issues when creating snapshots.

runtime/vm/snapshot.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart.h"
@@ skipping 1918 matching lines @@
   if (instructions_snapshot_buffer != NULL) {
     instructions_writer_ = new InstructionsWriter(instructions_snapshot_buffer,
                                                   alloc,
                                                   kInitialSize);
   }
 }
 
 
 FullSnapshotWriter::~FullSnapshotWriter() {
   delete forward_list_;
+  // We may run Dart code afterwards, restore the symbol table.
+  isolate()->object_store()->set_symbol_table(symbol_table_);
   symbol_table_ = Array::null();
   scripts_ = Array::null();
 }
 
 
 void FullSnapshotWriter::WriteVmIsolateSnapshot() {
   ASSERT(vm_isolate_snapshot_buffer_ != NULL);
   SnapshotWriter writer(Snapshot::kFull,
                         thread(),
                         vm_isolate_snapshot_buffer_,
@@ skipping 711 matching lines @@
   if (setjmp(*jump.Set()) == 0) {
     NoSafepointScope no_safepoint;
     WriteObject(obj.raw());
   } else {
     ThrowException(exception_type(), exception_msg());
   }
 }
 
 
 }  // namespace dart