Re-land: base: Replace PurgeAndTruncate with Shrink function.

base/memory/discardable_shared_memory_unittest.cc

Index: base/memory/discardable_shared_memory_unittest.cc
diff --git a/base/memory/discardable_shared_memory_unittest.cc b/base/memory/discardable_shared_memory_unittest.cc
index 74d19a64527187678a4109e01d85fa2b1b700e53..c8c0bb4051d4e004f93fbead1c63b2d4ccf7ab09 100644
--- a/base/memory/discardable_shared_memory_unittest.cc
+++ b/base/memory/discardable_shared_memory_unittest.cc
@@ -311,5 +311,21 @@ TEST(DiscardableSharedMemoryTest, MappedSize) {
   EXPECT_EQ(0u, memory.mapped_size());
 }
 
+#if defined(OS_POSIX) && !defined(OS_ANDROID)
+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