Currently GetStackSample doesn't support simulator, thus sampler is aware of
simulator, but since we are moving it out, it shouldn't have knowledge of
simulator. This patch moves the logic using simulator accessible
to Isolate::GetStackSample, so that it supports simulator.

BUG=v8:4956
LOG=n

Review-Url: https://codereview.chromium.org/1926863003
Cr-Commit-Position: refs/heads/master@{#35944}