Add descriptions of MemoryState

components/memory_coordinator/public/interfaces/child_memory_coordinator.mojom

Index: components/memory_coordinator/public/interfaces/child_memory_coordinator.mojom
diff --git a/components/memory_coordinator/public/interfaces/child_memory_coordinator.mojom b/components/memory_coordinator/public/interfaces/child_memory_coordinator.mojom
index f54a3da2a2ed326ac53c29785c6e9d2ac9509bbc..0c3e889e589a47360523de644a9e9d618760af01 100644
--- a/components/memory_coordinator/public/interfaces/child_memory_coordinator.mojom
+++ b/components/memory_coordinator/public/interfaces/child_memory_coordinator.mojom
@@ -4,10 +4,17 @@
 
 module memory_coordinator.mojom;
 
+// MemoryState is an indicator that processes can use to guide their memory
+// allocation policies. For example, a process that receives the suspended
+// state can use that as as signal to drop memory caches.
 enum MemoryState {
+  // The state is unknown.
   UNKNOWN = -1,
+  // No memory constraints.
   NORMAL = 0,
+  // Running and interactive but allocation should be throttled.
   THROTTLED = 1,
+  // Still resident in memory but core processing logic has been suspended.
   SUSPENDED = 2,
 };