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- This feature is behind the flag: PartitionAllocGigaCage.
- This feature is only available on 64bit chrome.
- Currently 32GB address space is reserved for PartitionAllocator.
  - 16Gbyte for direct map allocation (1 pool), and
  - 16Gbyte for normal buckets allocation (1 pool)
- Need to invoke PartitionAllocGlobalInit() before alllocating memory via PartitionAllocator.

Bug: 1086388
Change-Id: I370d2422e5f3ee5825334da3a4914730b0fbee93
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2174031
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774965}