Also SubDataOffsetPreservesContents.

BUG=angleproject:2185

Change-Id: I73401e4b511313f14ee9659f3d20c8086e3d04a3
Reviewed-on: https://chromium-review.googlesource.com/719890
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>