Bug 1661364 - Part 2: Don't recycle web processes with Fission enabled, r=kmag,jesup

It is uncommon to have long-lived "web" processes when Fission is enabled, so in
general we probably don't want to be performing content process recycling.

We also skip recycling web processes when E10s is disabled, as the process
preallocator would be disabled in that case, so recycling processes can lead to
mochitest-chrome test failures.

Differential Revision: https://phabricator.services.mozilla.com/D88626

dom/ipc/ContentParent.cpp

@@ -1980,6 +1980,12 @@ bool ContentParent::TryToRecycle() {
     return false;
   }
 
+  // Don't bother recycling "web" processes if Fission is enabled, as they
+  // should be largely unused.
+  if (mozilla::FissionAutostart()) {
+    return false;
+  }
+
   // This life time check should be replaced by a memory health check (memory
   // usage + fragmentation).