Revert "[macOS] PixelBufferPool: Test retaining IOSurface, not CVPixelBuffer."

This reverts commit be3eeb5b.

Reason for revert:

Findit (https://goo.gl/kROfz5) identified CL at revision 824814 as the
culprit for failures in the build cycles as shown on:
https://analysis.chromium.org/waterfall/culprit?key=ag9zfmZpbmRpdC1mb3ItbWVyRAsSDVdmU3VzcGVjdGVkQ0wiMWNocm9taXVtL2JlM2VlYjViMzk5NTY5YTZiMWQ4OGY5ZTk1M2M3NmIxNDQxMWJiYTEM

Sample Failed Build: https://ci.chromium.org/b/8864373521456164320

Sample Failed Step: capture_unittests

Original change's description:
> [macOS] PixelBufferPool: Test retaining IOSurface, not CVPixelBuffer.
> 
> Pixel buffers originating from a CVPixelBufferPool are recycled when
> no longer in use, previously only tested by releasing the last pixel
> buffer reference and not touching the IOSurface.
> 
> This CL tests what happens when we are retaining not references to the
> pixel buffer, but references to a pixel buffer's IOSurface or
> incrementing its use count.
> 
> Outcome:
> - Retaining references (base::ScopedCFTypeRef<IOSurfaceRef>) to an
>   IOSurface does NOT prevent recycling.
> - Retaining use count (IOSurfaceIncrementUseCount) to an IOSurface DOES
>   prevent recycling.
> 
> This behavior is now documented in pixel_buffer_pool_mac.h.
> 
> Bug: chromium:1132299
> Change-Id: Ibdcd3752a4467bc495eba4b543ecd73da1b2f41f
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2520829


> Commit-Queue: Markus Handell <handellm@google.com>
> Reviewed-by: Markus Handell <handellm@google.com>
> Cr-Commit-Position: refs/heads/master@{#824814}


Change-Id: I9ffde1dcd267cf97ed5918ba86e913189625f3e5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1132299
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2523054
Cr-Commit-Position: refs/heads/master@{#824891}