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The original CL caused two race conditions to trigger more frequently. These
have been fixed at
https://chromium-review.googlesource.com/c/chromium/src/+/917243.

> This CL cleans up both the public interface and private implementation of memory
> instrumentation. It is in preparation for allowing memory instrumentation to
> asynchronously add heap dumps to traces.
>
> memory_instrumentation supports two interfaces: HeapProfilerHelper and
> Coordinator [specifically RequestGlobalMemoryDump]. They are used by different
> clients, with different privileges, for different purposes. The internal
> implementation used a single code path to support both, which further results in
> leakage of implementation details into the mojom interface, in the form of
> LevelOfDetail::VM_REGIONS_ONLY_FOR_HEAP_PROFILER.
>
> The previous implementation only allowed 1 global dump to be issued at a time.
> This causes problems for my upcoming refactor, which makes
> memory_instrumentation, during a global dump, request a heap dump from the
> profiling service. The profiling service in turn requests heaps from
> memory_instrumentation, resulting in a deadlock.
>
> This CL updates the implementation of CoordinatorImpl to use a separate queue of
> |in_progress_vm_region_requests_| to track heap dump requests. These are
> executed as soon as they are received. This CL also removes
> LevelOfDetail::VM_REGIONS_ONLY_FOR_HEAP_PROFILER, and updates
> GetVmRegionsForHeapProfiler to explicitly specify PIDs to dump.
>
> Bug: 758739
> Change-Id: I4add68c2e3acc8eeb66d99731fce59063ac5e23f
> Reviewed-on: https://chromium-review.googlesource.com/900222
> Commit-Queue: Erik Chen <erikchen@chromium.org>
> Reviewed-by: Daniel Cheng <dcheng@chromium.org>
> Reviewed-by: Ilya Sherman <isherman@chromium.org>
> Reviewed-by: Primiano Tucci <primiano@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#536263}

Change-Id: I4add68c2e3acc8eeb66d99731fce59063ac5e23f
Bug: 758739
TBR: isherman@chromium.org, dcheng@chromium.org, primiano@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/916501
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536878}