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This reverts commit f99a085f.

Reason for revert: Broke iOS build

Original change's description:
> [Sampling profiler] Use cross-platform sampling implementation for Mac
> 
> Refactors the Mac sampling to use the StackSamplerImpl implementation,
> with the platform-specific aspects moved into ThreadDelegateMac.
> 
> Bug: 931418
> Change-Id: I8f468fa09b9ddc85921f21563ff41000a5c968f5
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1535178
> Reviewed-by: Lei Zhang <thestig@chromium.org>
> Reviewed-by: Leonard Grey <lgrey@chromium.org>
> Commit-Queue: Mike Wittman <wittman@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#644804}

TBR=thestig@chromium.org,wittman@chromium.org,lgrey@chromium.org

Change-Id: I3f50a2117449abca9c58d89b13febab3889b421b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 931418
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1541586Reviewed-by: Mike Wittman <wittman@chromium.org>
Commit-Queue: Mike Wittman <wittman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#644810}