Add heuristics to limit showing of new backspace UI bubble.

chrome/common/pref_names.cc

 // Copyright (c) 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/common/pref_names.h"
 
 #include "base/macros.h"
 #include "build/build_config.h"
 #include "chrome/common/pref_font_webkit_names.h"
 
@@ skipping 997 matching lines @@
 // asking the user to set up automatic updates when Keystone promotion is
 // required.
 const char kShowUpdatePromotionInfoBar[] =
     "browser.show_update_promotion_info_bar";
 #endif
 
 // Boolean that is false if we should show window manager decorations.  If
 // true, we draw a custom chrome frame (thicker title bar and blue border).
 const char kUseCustomChromeFrame[] = "browser.custom_chrome_frame";
 
+const char kBackShortcutBubbleShownCount[] =
+    "browser.back_shortcut_bubble_shown_count";
+
 #if defined(ENABLE_PLUGINS)
 // Which plugins have been whitelisted manually by the user.
 const char kContentSettingsPluginWhitelist[] =
     "profile.content_settings.plugin_whitelist";
 #endif
 
 // Double that indicates the default zoom level.
 const char kPartitionDefaultZoomLevel[] = "partition.default_zoom_level";
 
 // Dictionary that maps hostnames to zoom levels.  Hosts not in this pref will
@@ skipping 1189 matching lines @@
 const char kMediaRouterEnableCloudServices[] =
     "media_router.cloudservices.enabled";
 #endif  // defined(GOOGLE_CHROME_BUILD)
 // Whether or not the Media Router first run flow has been acknowledged by the
 // user.
 const char kMediaRouterFirstRunFlowAcknowledged[] =
     "media_router.firstrunflow.acknowledged";
 #endif
 
 }  // namespace prefs