Clean up after each MemoryCoordinatorImpl test

content/browser/memory/memory_coordinator_impl.cc

Index: content/browser/memory/memory_coordinator_impl.cc
diff --git a/content/browser/memory/memory_coordinator_impl.cc b/content/browser/memory/memory_coordinator_impl.cc
index 032a91d8333f926264a57292e0982b267b85603f..22afb7b3401ca267de5d008da9ea8596b15f3987 100644
--- a/content/browser/memory/memory_coordinator_impl.cc
+++ b/content/browser/memory/memory_coordinator_impl.cc
@@ -176,7 +176,9 @@ MemoryCoordinatorImpl::MemoryCoordinatorImpl(
   base::MemoryCoordinatorProxy::SetMemoryCoordinator(this);
 }
 
-MemoryCoordinatorImpl::~MemoryCoordinatorImpl() {}
+MemoryCoordinatorImpl::~MemoryCoordinatorImpl() {
+  base::MemoryCoordinatorProxy::SetMemoryCoordinator(nullptr);
+}
 
 void MemoryCoordinatorImpl::Start() {
   DCHECK(CalledOnValidThread());