This reverts commit 176a2b24.

Reason for revert: performance regression on the benchmarks.

Original change's description:
> [heap] Reland "[heap] Allow a minimum semi-space size of 512K."
> 
> This patch changes the semi-space size to 512K.
> 
> > Original commit message:
> > Revert "[heap] Allow a minimum semi-space size of 512K."
> > This reverts commit 0d2ed6c3.
> > The CL introduced perf regressions: crbug.com/735649.
> > We are going to reland the CL in an isolated V8 roll to ensure
> > that perf regressions are attributed correctly.
> 
> > Original commit message:
> > > [heap] Allow a minimum semi-space size of 512K.
> > > This CL also reduces the minimum semi-space size to 512K.
> > > BUG=chromium:716032
> > BUG=chromium:735649
> 
> Change-Id: Iabc377cba2911b28d51b98bb5b85134d4e893632
> Reviewed-on: https://chromium-review.googlesource.com/575066
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46763}

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

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I80f8b6699f41e91512f7cec38060c829252ff95e
Reviewed-on: https://chromium-review.googlesource.com/591309Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46982}