Add MemoryWedge to ios/.

ios/chrome/browser/memory/memory_wedge.cc

+// 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 "ios/chrome/browser/memory/memory_wedge.h"
+
+#include <stdlib.h>
+
+#include "base/logging.h"
+
+namespace {
+
+// Reference to the memory wedge. It is useful to:
+// - make sure the compiler optimizations in Release don't skip |memset| and
+//   really end up putting the wedge in resident memory;
+// - free it in tests.
+static void* gMemoryWedge;
+
+// The number of bytes in a megabyte.
+const size_t kNumBytesInMB = 1024 * 1024;
+
+}  // namespace
+
+namespace memory_wedge {
+
+void AddWedge(size_t wedge_size_in_mb) {
+  DCHECK(!gMemoryWedge);
+  if (wedge_size_in_mb == 0)
+    return;
+
+  // Allocate a wedge and write to it to have it in resident memory.
+  const size_t wedge_size = wedge_size_in_mb * kNumBytesInMB;
+  gMemoryWedge = malloc(wedge_size);
+  memset(gMemoryWedge, -1, wedge_size);
+}
+
+void RemoveWedgeForTesting() {
+  DCHECK(gMemoryWedge);
+  free(gMemoryWedge);
+  gMemoryWedge = nullptr;
+}
+
+}  // namespace memory_wedge