Instant: Use only one hidden WebContents per profile.

chrome/browser/instant/instant_overlay_controller.cc

Index: chrome/browser/instant/instant_overlay_controller.cc
diff --git a/chrome/browser/instant/instant_overlay_controller.cc b/chrome/browser/instant/instant_overlay_controller.cc
new file mode 100644
index 0000000000000000000000000000000000000000..b0b88181e031de49058bb6a63b66d1e6728b8513
--- /dev/null
+++ b/chrome/browser/instant/instant_overlay_controller.cc
@@ -0,0 +1,20 @@
+// 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.
+
+#include "chrome/browser/instant/instant_overlay_controller.h"
+
+#include "chrome/browser/instant/instant_controller.h"
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/browser_instant_controller.h"
+
+InstantOverlayController::InstantOverlayController(Browser* browser)
+    : browser_(browser) {
+  if (browser_->instant_controller())
+    browser_->instant_controller()->instant()->AddModelObserver(this);
+}
+
+InstantOverlayController::~InstantOverlayController() {
+  if (browser_->instant_controller())
+    browser_->instant_controller()->instant()->RemoveModelObserver(this);
+}