viz: Set SkiaOutputDeviceDComp max_pending_swaps based on buffer count

This change allows us to have two pending swaps in the case of triple
buffering. Previously it was hard-coded to one. This follows the pattern
found in the GL, BufferQueue, and Webview SkiaOutputDevices.

Change-Id: I52b49c118d49845b10db2582835a60e8588aaf01
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5879537
Commit-Queue: Michael Tang <tangm@microsoft.com>
Reviewed-by: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1362084}