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This reverts commit b86ebc88.

Reason for revert: Introduces flakiness due to removal of global StatisticsRecorder teardown - see crbug.com/798717. This is a cross-platyform issue but in practice only caused base_unittests failures on the Fuchsia FYI bots, presumably due to differences in test ordering.

Original change's description:
> Simplified and optimized StatisticsRecorder.
> 
> StatisticsRecorder is now an actual container of collections.
> 
> There is only one global recorder at any time, referenced by
> StatisticsRecorder::top_.
> 
> Each StatisticsRecorder also has a pointer to the previous global recorder.
> 
> We now have a stack (singly linked list) of StatisticsRecorder objects, where
> the top of the stack (StatisticsRecorder::top_) is the current global recorder.
> 
> This pattern is clearer and cleaner. It avoids a bunch of static variables,
> indirections, unique_ptrs and calls to operator new. It gets rid of the ugly
> hacks of UninitializeForTesting. It reduces memory fragmentation by having fewer
> dynamically allocated objects.
> 
> Removed methods Reset, UninitializeForTesting and DumpHistogramsToVlog. They are
> now unnecessary.
> 
> Reviewed, clarified and documented the thread safety status of each method.
> 
> Added comments.
> 
> 
> Change-Id: Ia1a7611905009d0449068c801464ad0df7813c0d
> Bug: 
> Reviewed-on: https://chromium-review.googlesource.com/830997
> Commit-Queue: François Degros <fdegros@chromium.org>
> Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#526570}

TBR=asvitkine@chromium.org,gayane@chromium.org,holte@chromium.org,skare@chromium.org,fdegros@chromium.org

Change-Id: I4bd60c636a821bf681eb452636ade1098d3a4899
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/848273Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526718}