Add ScopedKeepAlive to c/b/lifetime

chrome/browser/lifetime/scoped_keep_alive.h

Index: chrome/browser/lifetime/scoped_keep_alive.h
diff --git a/chrome/browser/lifetime/scoped_keep_alive.h b/chrome/browser/lifetime/scoped_keep_alive.h
new file mode 100644
index 0000000000000000000000000000000000000000..d48a698fc972859cdefb323b9d165bceb1700ee4
--- /dev/null
+++ b/chrome/browser/lifetime/scoped_keep_alive.h
@@ -0,0 +1,28 @@
+// 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.
+
+#ifndef CHROME_BROWSER_LIFETIME_SCOPED_KEEP_ALIVE_H_
+#define CHROME_BROWSER_LIFETIME_SCOPED_KEEP_ALIVE_H_
+
+#include <string>
+
+#include "base/macros.h"
+#include "chrome/browser/lifetime/keep_alive_registry.h"
+
+// Registers token with KeepAliveRegistry on creation and unregisters them
+// on destruction. Use with a scoped_ptr for easy management of the tokens.
+class ScopedKeepAlive {
+ public:
+  explicit ScopedKeepAlive(const std::string& token,

[Bernhard Bauer, 2016/02/19 17:39:28]

Explain what the token is for?

[dgn, 2016/02/19 18:04:28]

Done.

+                           OptimizationOptions opt = OptimizationOptions::NONE);

[Bernhard Bauer, 2016/02/19 17:39:28]

I'm not very happy about the default argument here -- I think I would rather
have every client think about what optimizations can be applied. I might even
prefer using a list of two-state enums, just to make sure that every reader of
the code sees which optimizations we're talking about (rather than e.g. using a
bitfield, where seeing just NONE doesn't tell the reader which possible
optimizations there are).

[dgn, 2016/02/19 19:14:23]

Okay. I'll remove the argument for now then, and add one back when I implement
the observer, since I'll have to revisit all the call sites to update the
arguments anyway. It probably makes more sense that way.

+  ~ScopedKeepAlive();
+
+ private:
+  std::string token_;
+  OptimizationOptions opt_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedKeepAlive);
+};
+
+#endif  // CHROME_BROWSER_LIFETIME_SCOPED_KEEP_ALIVE_H_