Add a static getter for ChildMemoryCoordinator

components/memory_coordinator/child/child_memory_coordinator_impl.h

Index: components/memory_coordinator/child/child_memory_coordinator_impl.h
diff --git a/components/memory_coordinator/child/child_memory_coordinator_impl.h b/components/memory_coordinator/child/child_memory_coordinator_impl.h
index 6e71d20b3b81aac0792d39d86053cfa6753cb6e4..b4af1f66a45ca99759e9920dda6d937a33737c4d 100644
--- a/components/memory_coordinator/child/child_memory_coordinator_impl.h
+++ b/components/memory_coordinator/child/child_memory_coordinator_impl.h
@@ -31,8 +31,11 @@ class MEMORY_COORDINATOR_EXPORT ChildMemoryCoordinatorImpl
     : public ClientRegistry,
       NON_EXPORTED_BASE(public mojom::ChildMemoryCoordinator) {
  public:
-  explicit ChildMemoryCoordinatorImpl(mojom::MemoryCoordinatorHandlePtr parent,
-                                      ChildMemoryCoordinatorDelegate* delegate);
+  // Returns the instance of ChildMemoryCoordinatorImpl. Could be nullptr.
+  static ChildMemoryCoordinatorImpl* GetInstance();
+
+  ChildMemoryCoordinatorImpl(mojom::MemoryCoordinatorHandlePtr parent,
+                             ChildMemoryCoordinatorDelegate* delegate);
   ~ChildMemoryCoordinatorImpl() override;
 
   // mojom::ChildMemoryCoordinator implementations: