Update from chromium https://crrev.com/301315

base/memory/discardable_memory_manager_unittest.cc

 // Copyright 2014 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.
 
 #include "base/memory/discardable_memory_manager.h"
 
 #include "base/bind.h"
 #include "base/synchronization/waitable_event.h"
 #include "base/threading/thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 15 matching lines @@
     return was_allocated;
   }
   void ReleaseLock() override {
     DCHECK(is_locked_);
     is_locked_ = false;
   }
   void Purge() override {
     DCHECK(is_allocated_);
     is_allocated_ = false;
   }
+  virtual bool IsMemoryResident() const override {
+    DCHECK(is_allocated_);
+    return true;
+  }
 
   bool is_locked() const { return is_locked_; }
 
  private:
   bool is_allocated_;
   bool is_locked_;
 };
 
 // Tests can assume that the default limit is at least 1024. Tests that rely on
 // something else needs to explicit set the limit.
@@ skipping 435 matching lines @@
            Unretained(this)));
   memory_usage_thread_.message_loop()->PostTask(
       FROM_HERE,
       Bind(&ThreadedDiscardableMemoryManagerTest::SignalHelper,
            Unretained(this)));
   thread_sync_.Wait();
 }
 
 }  // namespace
 }  // namespace base