This CL makes the following changes:
1) Size of allocated buffer is set by a template parameter
   (with a default value instead of hardcoded size)
2) Remove dynamic parameter for initializing number of
   tasks (see comment in scavenger.cc)

This CL aligns the v8 and oilpan heaps so that they provide
the same interface and functionality.

Change-Id: I77d63793f0a54ea29198ddd6bd298eae2c15cf42
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2030920Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66158}