chromeos: power: Refactor RendererFreezer and add tests

chrome/browser/chromeos/power/freezer_cgroup_process_manager.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/freezer_cgroup_process_manager.h"
+
+#include "base/files/file_util.h"
+#include "base/logging.h"
+
+namespace chromeos {
+
+namespace {
+const char kFreezerStatePath[] =
+    "/sys/fs/cgroup/freezer/chrome_renderers/freezer.state";
+const char kFreezeCommand[] = "FROZEN";
+const char kThawCommand[] = "THAWED";
+
+}  // namespace
+
+FreezerCgroupProcessManager::FreezerCgroupProcessManager()
+    : state_path_(base::FilePath(kFreezerStatePath)),
+      enabled_(base::PathIsWritable(state_path_)) {
+}
+
+FreezerCgroupProcessManager::~FreezerCgroupProcessManager() {
+}
+
+bool FreezerCgroupProcessManager::FreezeRenderers() {
+  if (!enabled_) {
+    LOG(ERROR) << "Attempting to freeze renderers when the freezer cgroup is "
+               << "not available.";
+    return false;
+  }
+
+  return base::WriteFile(state_path_, kFreezeCommand, strlen(kFreezeCommand)) ==

[Daniel Erat, 2014/09/12 22:53:22]

nit: i don't think that WriteFile logs any details about errors, so it might be
worthwhile adding a helper method, e.g.:

  bool WriteCommandToStateFile(const std::string& command) {
    int bytes = base::WriteFile(state_path_, command.c_str(), command.size());
    if (bytes == -1) {
      PLOG(ERROR) << "Writing " << command << " to " << state_path_ << "
failed";
      return false;
    } else if (bytes != command.size()) {
      LOG(ERROR) << "Only wrote " << bytes << " byte(s) when writing "
                 << command << " to " << state_path_;
      return false;
    }
    return true;
  }

(there really ought to be a helper function for this in file_util.h :-/)

+      static_cast<int>(strlen(kFreezeCommand));
+}
+
+bool FreezerCgroupProcessManager::ThawRenderers() {
+  if (!enabled_) {
+    LOG(ERROR) << "Attempting to thaw renderers when the freezer cgroup is not "
+               << "available.";
+    return false;
+  }
+
+  return base::WriteFile(state_path_, kThawCommand, strlen(kThawCommand)) ==
+      static_cast<int>(strlen(kThawCommand));
+}
+
+bool FreezerCgroupProcessManager::CanFreezeRenderers() {
+  return enabled_;
+}
+
+}  // namespace chromeos