chromeos: power: Refactor RendererFreezer and add tests

chrome/browser/chromeos/power/renderer_freezer_delegate.cc

+// Copyright 2014 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 "chrome/browser/chromeos/power/renderer_freezer_delegate.h"
+
+#include "base/files/file_util.h"
+
+namespace chromeos {
+
+namespace {
+const char kFreezerStatePath[] =
+    "/sys/fs/cgroup/freezer/chrome_renderers/freezer.state";
+const char kFreezeCommand[] = "FROZEN";
+const char kThawCommand[] = "THAWED";
+
+}  // namespace
+
+RendererFreezerDelegate::RendererFreezerDelegate()
+    : state_path_(base::FilePath(kFreezerStatePath)),
+      enabled_(base::PathExists(state_path_) &&

[Daniel Erat, 2014/09/06 02:01:25]

you should be able to just call PathIsWritable (which is access(..., W_OK)) here
without additionally calling PathExists (which is access(..., F_OK))

+               base::PathIsWritable(state_path_)) {
+}
+
+RendererFreezerDelegate::~RendererFreezerDelegate() {
+}
+
+bool RendererFreezerDelegate::FreezeRenderers() {

[Daniel Erat, 2014/09/06 02:01:25]

maybe DCHECK() or LOG(ERROR) and return early or something here if !enabled_?
ditto for ThawRenderers().

+  return base::WriteFile(state_path_, kFreezeCommand, strlen(kFreezeCommand)) ==
+      static_cast<int>(strlen(kFreezeCommand));
+}
+
+bool RendererFreezerDelegate::ThawRenderers() {
+  return base::WriteFile(state_path_, kThawCommand, strlen(kThawCommand)) ==
+      static_cast<int>(strlen(kThawCommand));
+}
+
+bool RendererFreezerDelegate::CanFreezeRenderers() {
+  return enabled_;
+}
+
+}  // namespace chromeos