alternate ntp: implement Show/HideBars API to reduce jank when showing/hiding bars

chrome/browser/instant/search.h

 // 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_SEARCH_H_
 #define CHROME_BROWSER_INSTANT_SEARCH_H_
 
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/string16.h"
 
 class GURL;
 class PrefRegistrySyncable;
 class Profile;
 class TemplateURL;
 class TemplateURLRef;
 
+namespace chrome {
+namespace search {
+struct Mode;
+}
+}
+
 namespace content {
 class NavigationEntry;
 class WebContents;
 }
 
 namespace chrome {
 namespace search {
 
 // The key used to store search terms data in the NavigationEntry to be later
 // displayed in the omnibox. With the context of the user's exact query,
@@ skipping 112 matching lines @@
 // Exposed for testing only.
 bool GetBoolValueForFlagWithDefault(const std::string& flag,
                                     bool default_value,
                                     const FieldTrialFlags& flags);
 
 // Coerces the commandline Instant URL to look like a template URL, so that we
 // can extract search terms from it. Exposed for testing only.
 GURL CoerceCommandLineURLToTemplateURL(const GURL& instant_url,
                                        const TemplateURLRef& ref);
 
+// Returns true if visibility change in top bars should be handled based on
+// |old_mode| and |new_mode|.
+bool ShouldHandleTopBarsVisibilityChange(const Mode& old_mode,

[dhollowa, 2013/03/13 17:21:55]

This should live in search_model.h/cc.  And how about renaming to
|ShouldChangeTopBarsVisibility|?

[kuan, 2013/03/13 22:21:07]

Done.

+                                         const Mode& new_mode);
+
 }  // namespace search
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_INSTANT_SEARCH_H_