Add PurgeMemory() method for ChildMemoryCoordinator.mojom

content/common/child_memory_coordinator.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module content.mojom;
 
 // See base/memory/memory_coordinator_client.h for the definitions of these
 // states.
 enum MemoryState {
   UNKNOWN = -1,
   NORMAL = 0,
   THROTTLED = 1,
   SUSPENDED = 2,
 };
 
 // ChildMemoryCoordinator lives in a child process and receives memory events
 // dispatched by the central memory coordinator which lives in the browser
 // process.
 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();
 };