Create interface "EventPageTracker" for checking an extension's

extensions/browser/event_page_tracker.h

Index: extensions/browser/event_page_tracker.h
diff --git a/extensions/browser/event_page_tracker.h b/extensions/browser/event_page_tracker.h
new file mode 100644
index 0000000000000000000000000000000000000000..eb475dd4fc0f2c68aa2ae5f74557d86705bfc8bd
--- /dev/null
+++ b/extensions/browser/event_page_tracker.h
@@ -0,0 +1,38 @@
+// Copyright 2015 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 EXTENSIONS_BROWSER_EVENT_PAGE_TRACKER_H_
+#define EXTENSIONS_BROWSER_EVENT_PAGE_TRACKER_H_
+
+#include <string>
+
+#include "base/callback.h"
+
+namespace extensions {
+
+class Extension;
+class ExtensionHost;
+
+// Tracks an extension's event page suspend state.
+class EventPageTracker {
+ public:
+  // Returns true if an extension's event page is active,
+  // or false if it is suspended.
+  virtual bool IsEventPageSuspended(const std::string& extension_id) = 0;
+
+  // Wakes an extension's event page from a suspended state and calls
+  // |callback| after it is reactivated.
+  //
+  // |callback| will be passed true if the extension was reactivated
+  // successfully, or false if an error occurred.
+  //
+  // Returns true if a wake operation was scheduled successfully,
+  // or false if the event page was already awake.

[not at google - send to devlin, 2015/04/28 21:35:11]

Add a comment to the effect of "|callback| will be run asynchronously if true,
and never run if false".

In light of that you may want to tweak the comment earlier "calls |callback|
after it is reactivated."

+  virtual bool WakeEventPage(const std::string& extension_id,
+                             const base::Callback<void(bool)>& callback) = 0;
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_BROWSER_EVENT_PAGE_TRACKER_H_