Fix corrupted glDepthMask in SkImage destructor

Quoting vasilyt:

So what happens:

* We made current virtual context of GLES2 Decoder.

* Someone deleted shared image SharedImageStub::OnDestroySharedImage.

* For performance reasons, SharedImageStub::MakeContextCurrent doesn't
switch virtual contexts, only real. It's done in assumptions, that we
don't really change GL state during it, just deleting resources (e.g
textures) [1].

* This assumption is wrong because of workaround (and maybe something
else) here [2]

This is similar to https://crbug.com/1095679, but in dtor. We need
context_state_->MakeCurrent(nullptr); in the beginning of
~WrappedSkImage [3]

What is interesting -- there is DCHECK for context_state_->IsCurrent(),
but if I read code correctly, that only checks for real context to be
current and I'm not sure if that's right.

[1] https://source.chromium.org/chromium/chromium/src/+/master:gpu/ipc/service/shared_image_stub.cc;drc=8cd33c0a2ffc73d284354e431687011534e29fb8;l=458

[2] https://source.chromium.org/chromium/chromium/src/+/master:third_party/skia/src/gpu/gl/GrGLGpu.cpp;drc=ae67c52933d2da6ea7b9cdff251738487bb84c74;l=2941

[3] https://source.chromium.org/chromium/chromium/src/+/master:gpu/command_buffer/service/wrapped_sk_image.cc;drc=67a4fbcab976e3c625bd241e10c3c3bed305137e;l=54

Bug: 1167450,1184085
Change-Id: I6577b0d59575e499b92bda9f31dcfec4eca2f5d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2729901
Commit-Queue: Klaus Weidner <klausw@chromium.org>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#859662}