Add discardable memory emulation for non-android/mac platforms

base/memory/discardable_memory_mac.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 <mach/mach.h>
 
 #include "base/logging.h"
 
 namespace base {
 
 namespace {
 
 // The VM subsystem allows tagging of memory and 240-255 is reserved for
 // application use (see mach/vm_statistics.h). Pick 252 (after chromium's atomic
 // weight of ~52).
 const int kDiscardableMemoryTag = VM_MAKE_TAG(252);
 
 }  // namespace
 
 // static
-bool DiscardableMemory::Supported() {
+bool DiscardableMemory::SupportedNatively() {
   return true;
 }
 
 DiscardableMemory::~DiscardableMemory() {
   if (memory_) {
     vm_deallocate(mach_task_self(),
                   reinterpret_cast<vm_address_t>(memory_),
                   size_);
   }
 }
@@ skipping 59 matching lines @@
   return true;
 }
 
 // static
 void DiscardableMemory::PurgeForTesting() {
   int state = 0;
   vm_purgable_control(mach_task_self(), 0, VM_PURGABLE_PURGE_ALL, &state);
 }
 
 }  // namespace base