athena: Add the concept of Activity and related managers.

athena/main/placeholder_content.h

Index: athena/main/placeholder_content.h
diff --git a/athena/main/placeholder_content.h b/athena/main/placeholder_content.h
new file mode 100644
index 0000000000000000000000000000000000000000..404a4e726b46b01dd5de5c0cdf3936effbe611e8
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+++ b/athena/main/placeholder_content.h
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+// 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 ATHENA_MAIN_PLACEHOLDER_CONTENT_H_
+#define ATHENA_MAIN_PLACEHOLDER_CONTENT_H_
+
+namespace content {
+class BrowserContext;
+}
+
+// Creates WebContents with a pre-defined set of windows.
+void CreateTestPages(content::BrowserContext* browser_context);
+
+#endif  // ATHENA_MAIN_PLACEHOLDER_CONTENT_H_