Add discardable memory emulation for non-android/mac platforms

base/memory/discardable_memory_unittest.cc

Index: base/memory/discardable_memory_unittest.cc
diff --git a/base/memory/discardable_memory_unittest.cc b/base/memory/discardable_memory_unittest.cc
index 60d35820fbd489a2fea3c9d9af70eb6195a5df0a..6c327ae4f56fd470e62869d4e1985b937249076e 100644
--- a/base/memory/discardable_memory_unittest.cc
+++ b/base/memory/discardable_memory_unittest.cc
@@ -7,11 +7,20 @@
 
 namespace base {
 
-#if defined(OS_ANDROID) || defined(OS_MACOSX)
+TEST(DiscardableMemoryTest, SupportedNatively) {
+#if defined(DISCARDABLE_MEMORY_ALWAYS_SUPPORTED_NATIVELY)
+  ASSERT_TRUE(DiscardableMemory::SupportedNatively());
+#else
+  // If we ever have a platform that decides at runtime if it can support
+  // discardable memory natively, then we'll have to add a 'never supported
+  // natively' define for this case. At present, if it's not always supported
+  // natively, it's never supported.
+  ASSERT_FALSE(DiscardableMemory::SupportedNatively());
+#endif
+}
+
 // Test Lock() and Unlock() functionalities.
 TEST(DiscardableMemoryTest, LockAndUnLock) {
-  ASSERT_TRUE(DiscardableMemory::Supported());
-
   const size_t size = 1024;
 
   DiscardableMemory memory;
@@ -31,18 +40,15 @@ TEST(DiscardableMemoryTest, LockAndUnLock) {
 
 // Test delete a discardable memory while it is locked.
 TEST(DiscardableMemoryTest, DeleteWhileLocked) {
-  ASSERT_TRUE(DiscardableMemory::Supported());
-
   const size_t size = 1024;
 
   DiscardableMemory memory;
   ASSERT_TRUE(memory.InitializeAndLock(size));
 }
 
-#if defined(OS_MACOSX)
+#if !defined(OS_ANDROID)
 // Test forced purging.
 TEST(DiscardableMemoryTest, Purge) {
-  ASSERT_TRUE(DiscardableMemory::Supported());
   ASSERT_TRUE(DiscardableMemory::PurgeForTestingSupported());
 
   const size_t size = 1024;
@@ -54,8 +60,6 @@ TEST(DiscardableMemoryTest, Purge) {
   DiscardableMemory::PurgeForTesting();
   EXPECT_EQ(DISCARDABLE_MEMORY_PURGED, memory.Lock());
 }
-#endif  // OS_MACOSX
-
-#endif  // OS_*
+#endif  // !OS_ANDROID
 
 }