Revert "Share one GLContext for all RasterDecoder when virtual context is used."

This reverts commit 1808a743048d147521eaffb386dc9f29b4ecae0e.

Reason for revert: Null-dereference READ in gpu::gles2::ContextState::api
https://crbug.com/912981

Original change's description:
> Share one GLContext for all RasterDecoder when virtual context is used.
> 
> With this CL, we will create a GLContextVirtual in RasterDecoderContextState,
> and share it with all raster decoders, display compositoer, etc. It is a
> temporary solution. In follow up CLs, we will share the one GLContext with
> GLES2 as well. In that case, we will use GLContext directly instead of
> GLContextVirtual.
> 
> Change-Id: If9b8d1f32e58b32a9d9f8cd07aa10c30432e3183
> Bug: 902904
> Reviewed-on: https://chromium-review.googlesource.com/c/1357463
> Commit-Queue: Peng Huang <penghuang@chromium.org>
> Reviewed-by: Antoine Labour <piman@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#614694}

TBR=penghuang@chromium.org,piman@chromium.org

Change-Id: I2eb66f211d408988f30bfb870425da80e0eb7a4b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 902904
Reviewed-on: https://chromium-review.googlesource.com/c/1368284
Reviewed-by: Peng Huang <penghuang@chromium.org>
Commit-Queue: Peng Huang <penghuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614738}
18 files changed