The "version 0" format did not deal with references, and used a stack model to
deserialize objects (conceptually, a postorder tree traversal). This requires
an explicit stack, so special logic is added to decode this format.

All subsequent versions also put an object marker at the beginning, which is
equivalent to how the current version serializes.

BUG=chromium:148757

Review-Url: https://codereview.chromium.org/2248893003
Cr-Commit-Position: refs/heads/master@{#38686}