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..2d34a15345dec3b1d2aa3b7fbe2ff457dc1638f0 100644
--- a/base/memory/discardable_shared_memory_unittest.cc
+++ b/base/memory/discardable_shared_memory_unittest.cc
@@ -311,5 +311,22 @@ TEST(DiscardableSharedMemoryTest, MappedSize) {
   EXPECT_EQ(0u, memory.mapped_size());
 }
 
+TEST(DiscardableSharedMemoryTest, Shrink) {
+  if (!DiscardableSharedMemory::IsShrinkingSupported())

[danakj, 2015/03/18 23:18:52]

Do you think you could add platform #ifs here instead of early out based on
production code? Maybe you can verify this IsShrinkingSupported thing does what
you want too, to make people notice this test if they change that function?

[reveman, 2015/03/19 02:21:54]

I removed IsShrinkingSupported from latest patch and added #ifs around Shrink()
instead. That keeps things simple and I think it's more consistent with other
classes in base/ such as SharedMemory. PTAL.

+    return;
+
+  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());
+}
+
 }  // namespace
 }  // namespace base