update_engine: uint64_t GetPartitionSize() am: 6db5f79c67

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3248295

Change-Id: I2dc706ddc09df7e7f432b1bdc8f3f49ef71081c7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>