Crash when a process node is destroyed while still hosting worker nodes

This is a temporary CHECK() to help diagnose an existing crash.

The goal is to turn it into a dcheck once the issue is solved.

Bug: 1058705
Change-Id: I985d38759dcbfdd00ccdea896c1630fa925cf35f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2097175
Commit-Queue: Sigurður Ásgeirsson <siggi@chromium.org>
Reviewed-by: Sigurður Ásgeirsson <siggi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749162}

components/performance_manager/graph/process_node_impl.cc

@@ -22,6 +22,10 @@ ProcessNodeImpl::ProcessNodeImpl(GraphImpl* graph,
 
 ProcessNodeImpl::~ProcessNodeImpl() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+  // Crash if this process node is destroyed while still hosting a worker node.
+  // TODO(https://crbug.com/1058705): Turn this into a DCHECK once the issue is
+  //                                  resolved.
+  CHECK(worker_nodes_.empty());
 }
 
 void ProcessNodeImpl::Bind(