Instant: Use only one hidden WebContents per profile.

chrome/browser/instant/instant_service_observer.h

Index: chrome/browser/instant/instant_service_observer.h
diff --git a/chrome/browser/instant/instant_service_observer.h b/chrome/browser/instant/instant_service_observer.h
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+++ b/chrome/browser/instant/instant_service_observer.h
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+// Copyright 2013 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_SERVICE_OBSERVER_H_
+#define CHROME_BROWSER_INSTANT_INSTANT_SERVICE_OBSERVER_H_
+
+// This class defines the observer interface for InstantService.
+class InstantServiceObserver {
+ public:
+  // Indicates that either IsInstantEnabled() or IsInstantPrefEnabled() (as per
+  // chrome/browser/ui/search/search.h) has changed in value.
+  virtual void InstantStatusChanged() = 0;
+
+  // Indicates that the user's custom theme has changed in some way.
+  virtual void ThemeInfoChanged() = 0;
+
+  // Indicates that the Top Sites (Most Visited) info has changed in some way.
+  virtual void MostVisitedItemsChanged() = 0;
+
+ protected:
+  ~InstantServiceObserver() {}
+};
+
+#endif  // CHROME_BROWSER_INSTANT_INSTANT_SERVICE_OBSERVER_H_