This reverts commit 69a502ce.

Reason for revert: Broke the build https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8%20Linux%20gcc%204.8/22123

Original change's description:
> [heap profiler] Refactor: Replace indices with HeapEntry*
> 
> Change-Id: I0c176f66711d45e2f59d527f3133a1afbf825ec3
> Reviewed-on: https://chromium-review.googlesource.com/1229613
> Commit-Queue: Alexei Filippov <alph@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#56245}

TBR=ulan@chromium.org,alph@chromium.org,mlippautz@chromium.org

Change-Id: Ib4495f17a653a95f8d5af634da74905c63048f8e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/1246235Reviewed-by: Alexei Filippov <alph@chromium.org>
Commit-Queue: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56248}