When logging with --logfile-per-isolate, we use isolate addresses
to disambiguate. However, it often happens that the isolate addresses
are identical for different renderers, so we corrupt the log files.

This CL adds pid to the log filename when --logfile-per-isolate is on.

Bug: v8:8674
Change-Id: Id664b17d4dbaad2d805379dbe17ecbe08e4ae1f4
Reviewed-on: https://chromium-review.googlesource.com/c/1405853Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58746}