Update from chromium https://crrev.com/301315

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 "base/logging.h"
 #include "base/memory/discardable_memory_emulated.h"
 #include "base/memory/discardable_memory_mach.h"
 #include "base/memory/discardable_memory_manager.h"
+#include "base/memory/discardable_memory_shmem.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace base {
 
 // static
+void DiscardableMemory::ReleaseFreeMemory() {
+  internal::DiscardableMemoryShmem::ReleaseFreeMemory();
+}
+
+// static
 bool DiscardableMemory::ReduceMemoryUsage() {
   return internal::DiscardableMemoryEmulated::ReduceMemoryUsage();
 }
 
 // static
 void DiscardableMemory::GetSupportedTypes(
     std::vector<DiscardableMemoryType>* types) {
   const DiscardableMemoryType supported_types[] = {
     DISCARDABLE_MEMORY_TYPE_MACH,
-    DISCARDABLE_MEMORY_TYPE_EMULATED
+    DISCARDABLE_MEMORY_TYPE_EMULATED,
+    DISCARDABLE_MEMORY_TYPE_SHMEM
   };
   types->assign(supported_types, supported_types + arraysize(supported_types));
 }
 
 // static
 scoped_ptr<DiscardableMemory> DiscardableMemory::CreateLockedMemoryWithType(
     DiscardableMemoryType type, size_t size) {
   switch (type) {
     case DISCARDABLE_MEMORY_TYPE_MACH: {
       scoped_ptr<internal::DiscardableMemoryMach> memory(
           new internal::DiscardableMemoryMach(size));
       if (!memory->Initialize())
         return nullptr;
 
       return memory.Pass();
     }
     case DISCARDABLE_MEMORY_TYPE_EMULATED: {
       scoped_ptr<internal::DiscardableMemoryEmulated> memory(
           new internal::DiscardableMemoryEmulated(size));
       if (!memory->Initialize())
         return nullptr;
 
       return memory.Pass();
     }
+    case DISCARDABLE_MEMORY_TYPE_SHMEM: {
+      scoped_ptr<internal::DiscardableMemoryShmem> memory(
+          new internal::DiscardableMemoryShmem(size));
+      if (!memory->Initialize())
+        return nullptr;
+
+      return memory.Pass();
+    }
     case DISCARDABLE_MEMORY_TYPE_NONE:
     case DISCARDABLE_MEMORY_TYPE_ASHMEM:
       NOTREACHED();
       return nullptr;
   }
 
   NOTREACHED();
   return nullptr;
 }
 
 // static
 void DiscardableMemory::PurgeForTesting() {
   internal::DiscardableMemoryMach::PurgeForTesting();
   internal::DiscardableMemoryEmulated::PurgeForTesting();
+  internal::DiscardableMemoryShmem::PurgeForTesting();
 }
 
 }  // namespace base