Re-land: base: Use MADV_REMOVE instead of ftruncate to purge discardable memory segments.

base/memory/discardable_shared_memory_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/basictypes.h"
 #include "base/memory/discardable_shared_memory.h"
 #include "base/process/process_metrics.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
@@ skipping 325 matching lines @@
   memory.SetNow(Time::FromDoubleT(1));
   memory.Unlock(0, 0);
 
   // Lock and unlock memory.
   auto lock_rv = memory.Lock(0, 0);
   EXPECT_EQ(DiscardableSharedMemory::SUCCESS, lock_rv);
   memory.SetNow(Time::FromDoubleT(2));
   memory.Unlock(0, 0);
 }
 
-#if defined(DISCARDABLE_SHARED_MEMORY_SHRINKING)
-TEST(DiscardableSharedMemoryTest, Shrink) {
-  const uint32 kDataSize = 1024;
-
-  TestDiscardableSharedMemory memory;
-  bool rv = memory.CreateAndMap(kDataSize);
-  ASSERT_TRUE(rv);
-
-  EXPECT_NE(0u, memory.mapped_size());
-
-  // Mapped size should be 0 after shrinking memory segment.
-  memory.Shrink();
-  EXPECT_EQ(0u, memory.mapped_size());
-}
-#endif
-
 }  // namespace
 }  // namespace base