Add discardable memory emulation for non-android/mac platforms

base/memory/discardable_memory_unittest.cc

 // Copyright (c) 2013 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.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 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;
   ASSERT_TRUE(memory.InitializeAndLock(size));
   void* addr = memory.Memory();
   ASSERT_NE(static_cast<void*>(NULL), addr);
 
   memory.Unlock();
   // The system should have no reason to purge discardable blocks in this brief
   // interval, though technically speaking this might flake.
   EXPECT_EQ(DISCARDABLE_MEMORY_SUCCESS, memory.Lock());
   addr = memory.Memory();
   ASSERT_NE(static_cast<void*>(NULL), addr);
 
   memory.Unlock();
 }
 
 // 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;
 
   DiscardableMemory memory;
   ASSERT_TRUE(memory.InitializeAndLock(size));
   memory.Unlock();
 
   DiscardableMemory::PurgeForTesting();
   EXPECT_EQ(DISCARDABLE_MEMORY_PURGED, memory.Lock());
 }
-#endif  // OS_MACOSX
-
-#endif  // OS_*
+#endif  // !OS_ANDROID
 
 }