This reverts commit b0ced926.

Reason for revert: Build breakage - https://build.chromium.org/p/client.v8/builders/V8%20Linux/builds/20832

Original change's description:
> Track committed array buffer size rather than allocation length
> 
> WebAssembly creates ArrayBuffers with large allocations where only a small
> amount is committed. The uncommitted address space should not be counted as used
> memory. Doing so can lead to the GC spending unnecessary time collecting memory
> when there is not really pressure.
> 
> Bug: 
> Change-Id: Ife7b84e9858e87faabc360a61f887b2fda6d99db
> Reviewed-on: https://chromium-review.googlesource.com/710227
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Eric Holk <eholk@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#48462}

TBR=mlippautz@chromium.org,eholk@chromium.org

Change-Id: Ib7b28a7bbc8ffc11e0bf8c4bb16b2da61cbdbd5f
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/712835Reviewed-by: Eric Holk <eholk@chromium.org>
Commit-Queue: Eric Holk <eholk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48466}