How did it take for you to receive a review from ACM Computing Surveys?
I have not submitted to this journal in a long time, but I have reviewed for them on occasion.
ACM Computing Surveys publishes (typically long and intricate) survey papers. Consequently, they give the authors (for computer science) relatively long time to review (by default 8 weeks I believe). Additionally, it's not a stretch to believe that finding reviewers for such papers is even more difficult than for normal research articles.
In general, 4 - 6 months until first decision is fairly normal for a high-profile computer science journal. I don't see anything out of the expected in what you describe.
Is that indicative of my chances of being accepted for submission?
No. Review time is not indicative of your chances to get accepted (outside of the obvious case of a quick desk reject). Weak papers take approximately as long to review as very strong ones, and the main driver of delays is anyway how long it takes the editor to herd together a sufficient number of reviewers.
If anything, a long review time is indicative that your topic is sufficiently niche (or you have enough conflicts of interest) that the editor is struggling more than usual to find reviewers. But the Editor-in-Chief already told you as much.
