Beginnings of the script bubble.

chrome/common/extensions/feature_switch.h

+// Copyright (c) 2012 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_COMMON_EXTENSIONS_FEATURE_SWITCH_H_
+#define CHROME_COMMON_EXTENSIONS_FEATURE_SWITCH_H_
+
+#include "base/basictypes.h"
+
+class CommandLine;
+
+namespace extensions {
+
+// A switch that can turn a feature on or off. Typically controlled via
+// command-line switches but can be overridden, e.g., for testing.
+class FeatureSwitch {
+ public:
+  static FeatureSwitch* GetScriptBubble();
+
+  // A temporary override for the switch value.
+  class ScopedOverride {

[Jeffrey Yasskin, 2012/10/02 00:26:31]

You should DISALLOW_COPY_AND_ASSIGN on this or it's pretty easy to accidentally
set the FeatureSwitch back to its default. I'd probably make the constructor
public and remove FeatureSwitch::Override, especially since
"the_feature->Override(true);" has no effect but would compile fine in your
version.

[Aaron Boodman, 2012/10/02 01:28:52]

good point, done.

+   public:
+    ~ScopedOverride();
+   private:
+    friend FeatureSwitch;
+    ScopedOverride(FeatureSwitch* feature, bool override_value);
+    FeatureSwitch* feature_;
+    bool previous_value_;
+  };
+
+  enum DefaultValue {
+    DEFAULT_ENABLED,
+    DEFAULT_DISABLED
+  };
+
+  FeatureSwitch(const CommandLine* command_line,
+                const char* switch_name,
+                DefaultValue default_value);
+
+  bool IsEnabled() const;
+  ScopedOverride Override(bool override_value);
+
+ private:
+  enum OverrideValue {
+    OVERRIDE_NONE,
+    OVERRIDE_ENABLED,
+    OVERRIDE_DISABLED
+  };
+
+  void SetOverrideValue(OverrideValue value);
+
+  const CommandLine* command_line_;
+  const char* switch_name_;
+  bool default_value_;
+  OverrideValue override_value_;
+
+  DISALLOW_COPY_AND_ASSIGN(FeatureSwitch);
+};
+
+}  // namespace extensions
+
+#endif  // CHROME_COMMON_EXTENSIONS_FEATURE_SWITCH_H_