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Changes: disabled the thread cache on Windows.

Original change's description:
> base/allocator: Add a thread cache to PartitionAlloc.
>
> This CL adds a thread cache to PartitionAlloc. It is optional, only
> applies to thread-safe partitions, and uses the same freelist encoding
> and bucketing as the main allocator.
>
> The thread cache is added "in the middle" of the main allocator, that is:
> - After all the cookie/tag management
> - Before the "raw" allocator.
>
> That is, the general allocation flow is:
> 1. Adjustment of requested size to make room for tags / cookies
> 2. Allocation:
>   a. Call to the thread cache, if it succeeds, return.
>   b. Otherwise, call the "raw" allocator <-- Locking
> 3. Handle cookies/tags, zero allocation if required
>
> On the deallocation side, the process is reversed:
> 1. Check cookies / tags, adjust the pointer
> 2. Deallocation
>   a. Return to the thread cache of possible. If it succeeds, return.
>   b. Otherwise, call the "raw" allocator <-- Locking
>
> The thread cache maintains an array of buckets, the same as the parent
> allocator. A single thread cache instance is only used by a single
> partition. Each bucket is a linked list of allocations, capped to a set
> maximum size. Elements in this "freelist" are encoded the same way they
> are for the main allocator.
> Only the smallest buckets are eligible for caching, to reduce the
> memory impact.
>
> There are several limitations:
> - Only a single partition is allowed to have a thread cache
> - No periodic purging of thread caches is done
> - No statistics are collected
>
> The last two limitations will be addressed in subsequent CLs. Regarding
> the first one, it is not possible to use Chrome's native thread local
> storage support, as it allocates. It is also desirable to use
> thread_local to improve performance.
>
> Bug: 998048
> Change-Id: Ia771f507d9dd1c2c26a4668c76da220fb0c65dd4
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2375206
> Commit-Queue: Benoit L <lizeb@chromium.org>
> Reviewed-by: Kentaro Hara <haraken@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#805697}

Bug: 998048
Change-Id: I23b70f6964bb297502921d1a08bf128d9093d577
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2404849Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Commit-Queue: Benoit L <lizeb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806597}