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Mask layer's occlusion is actually its render surface's occlusion in the
contributed parent surface space.

However, when tiling a solid color mask layer, we used to adopt the logic
from normal picture layers: overwrite the occlusion's transform with the
layer's draw transform. This is problematic because mask layer's draw
transform is to the render surface that owns the mask. In this way, we
can generate the wrong visible quad rect and result in blanks when
rendering.

Since solid color mask layer does not do anything but cannot be fully
avoided in the current code base, we should never apply an occlusion to
it. Any occlusion to the masked content can still take effect by
applying itself to the owning render surface.

Bug: 811143, 810820, 808372
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel
Change-Id: I821492c107c2abadb9b9e6986369c9f6262d0ad4
Reviewed-on: https://chromium-review.googlesource.com/916625
Commit-Queue: Xianda Sun <sunxd@chromium.org>
Reviewed-by: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537794}