Update to new update_metadata.proto which support COW merge operation.

Now update_metadata.js will be able to parse COW merge operations in the
OTA packages. Please refer to change 1736935 for more details.

No-Typo-Check: auto-generated artifacts

Test: Mannual tested.
Change-Id: Ie18125524b991173b0599704eca51004fd0c0243
2 files changed