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In layer compositor and display compositor, only child ResourceProvider and
parent ResourceProvider are used. No grandparent ResourceProvider is being
used in real world except this unittests.

To align with the layer tree ResourceProvider and display ResourceProvider,
remove these grandparent related cases.

BUG=738190

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I31c4569885a2392d6925967d6db56ac9a3d78e58
Reviewed-on: https://chromium-review.googlesource.com/595115
Commit-Queue: Xing Xu <xing.xu@intel.com>
Reviewed-by: danakj <danakj@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491599}