base: Rename discardable memory allocator interface and remove unnecessary class.

base/memory/discardable_memory_allocator.cc

Index: base/memory/discardable_memory_allocator.cc
diff --git a/base/memory/discardable_memory_allocator.cc b/base/memory/discardable_memory_allocator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..002a3ba5e4763c360dc0a96861d0c53758bdb3bc
--- /dev/null
+++ b/base/memory/discardable_memory_allocator.cc
@@ -0,0 +1,34 @@
+// Copyright 2015 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_allocator.h"
+
+#include "base/logging.h"
+
+namespace base {
+namespace {
+
+DiscardableMemoryAllocator* g_allocator = nullptr;
+
+}  // namespace
+
+// static
+void DiscardableMemoryAllocator::SetInstance(
+    DiscardableMemoryAllocator* allocator) {
+  DCHECK(allocator);
+
+  // Make sure this function is only called once before the first call
+  // to GetInstance().
+  DCHECK(!g_allocator);
+
+  g_allocator = allocator;
+}
+
+// static
+DiscardableMemoryAllocator* DiscardableMemoryAllocator::GetInstance() {
+  DCHECK(g_allocator);
+  return g_allocator;
+}
+
+}  // namespace base