Instant: Use only one hidden WebContents per profile.

chrome/browser/instant/instant_overlay_controller.h

Index: chrome/browser/instant/instant_overlay_controller.h
diff --git a/chrome/browser/instant/instant_overlay_controller.h b/chrome/browser/instant/instant_overlay_controller.h
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+++ b/chrome/browser/instant/instant_overlay_controller.h
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+// Copyright 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_BROWSER_INSTANT_INSTANT_OVERLAY_CONTROLLER_H_
+#define CHROME_BROWSER_INSTANT_INSTANT_OVERLAY_CONTROLLER_H_
+
+#include "base/compiler_specific.h"
+#include "chrome/browser/instant/instant_model_observer.h"
+
+class Browser;
+class InstantModel;
+
+// Abstract base class for platform-specific Instant overlay controllers.
+class InstantOverlayController : public InstantModelObserver {
+ protected:
+  explicit InstantOverlayController(Browser* browser);
+  virtual ~InstantOverlayController();
+
+  Browser* const browser_;
+
+ private:
+  // Overridden from InstantModelObserver:
+  virtual void OverlayStateChanged(const InstantModel& model) OVERRIDE = 0;
+};
+
+#endif  // CHROME_BROWSER_INSTANT_INSTANT_OVERLAY_CONTROLLER_H_