Restore some DCHECKs in child process launcher.

BUG=1314491,469248

Change-Id: I22e7466635dae7a44c3a4b49d2fe20c021bb0825
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3580128
Auto-Submit: Will Harris <wfh@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#990864}

content/browser/child_process_launcher.cc

@@ -135,14 +135,12 @@ void ChildProcessLauncher::Notify(ChildProcessLauncherHelper::Process process,
 }
 
 bool ChildProcessLauncher::IsStarting() {
-  // TODO(crbug.com/469248): This fails in some tests.
-  // DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   return starting_;
 }
 
 const base::Process& ChildProcessLauncher::GetProcess() const {
-  // TODO(crbug.com/469248): This fails in some tests.
-  // DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   return process_.process;
 }