Add PurgeMemory() method for ChildMemoryCoordinator.mojom

content/common/child_memory_coordinator.mojom

Index: content/common/child_memory_coordinator.mojom
diff --git a/content/common/child_memory_coordinator.mojom b/content/common/child_memory_coordinator.mojom
index 0a20b7fbd3fce8589a4d74b99cfa8c83f3bf40ba..fe2d4f31257eeecc06802f5b8a8717162a52b866 100644
--- a/content/common/child_memory_coordinator.mojom
+++ b/content/common/child_memory_coordinator.mojom
@@ -20,4 +20,8 @@ interface ChildMemoryCoordinator {
   // Called when the central memory coodinator changes the state for child
   // processes.
   OnStateChange(MemoryState state);
+
+  // Requests the child process to purge memory (e.g. by dropping caches that
+  // can be easily rebuilt).
+  PurgeMemory();
 };