[logging] Add process id to filename when logging per isolate.

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}

src/log.cc

@@ -1869,10 +1869,12 @@ void Logger::LogAllMaps() {
 
 static void AddIsolateIdIfNeeded(std::ostream& os,  // NOLINT
                                  Isolate* isolate) {
-  if (FLAG_logfile_per_isolate) os << "isolate-" << isolate << "-";
+  if (FLAG_logfile_per_isolate) {
+    os << "isolate-" << isolate << "-" << base::OS::GetCurrentProcessId()
+       << "-";
+  }
 }
 
-
 static void PrepareLogFileName(std::ostream& os,  // NOLINT
                                Isolate* isolate, const char* file_name) {
   int dir_separator_count = 0;