Add discardable memory emulation for non-android/mac platforms

base/memory/discardable_memory_android.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 <sys/mman.h>
 #include <unistd.h>
 
 #include "base/lazy_instance.h"
@@ skipping 12 matching lines @@
 
 // Upper limit on the number of discardable memory to avoid hitting file
 // descriptor limit.
 const int kDiscardableMemoryNumLimit = 128;
 
 }
 
 namespace base {
 
 // static
-bool DiscardableMemory::Supported() {
+bool DiscardableMemory::SupportedNatively() {
   return true;
 }
 
 DiscardableMemory::~DiscardableMemory() {
   if (is_locked_)
     Unlock();
   // If fd_ is smaller than 0, initialization must have failed and
   // g_num_discardable_memory is not incremented by the caller.
   if (fd_ < 0)
     return;
@@ skipping 111 matching lines @@
 bool DiscardableMemory::PurgeForTestingSupported() {
   return false;
 }
 
 // static
 void DiscardableMemory::PurgeForTesting() {
   NOTIMPLEMENTED();
 }
 
 }  // namespace base