alternate ntp: fix website page jankiness when suggestions show and top bars are hidden

chrome/browser/ui/views/frame/contents_container.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_UI_VIEWS_FRAME_CONTENTS_CONTAINER_H_
 #define CHROME_BROWSER_UI_VIEWS_FRAME_CONTENTS_CONTAINER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "chrome/common/instant_types.h"
 #include "chrome/common/search_types.h"
+#include "ui/views/controls/webview/webview.h"
 #include "ui/views/view.h"
 
 namespace content {
 class WebContents;
 }
 
 namespace gfx {
 class Rect;
 }
 
-namespace views {
-class WebView;
-}
-
 // ContentsContainer is responsible for managing the WebContents views.
 // ContentsContainer has up to two children: one for the currently active
 // WebContents and one for Instant's WebContents.
 class ContentsContainer : public views::View {
  public:
   // Internal class name
   static const char kViewClassName[];
 
   explicit ContentsContainer(views::WebView* active);
   virtual ~ContentsContainer();
@@ skipping 11 matching lines @@
                   bool draw_drop_shadow);
 
   // When the active content is reset and we have a visible preview,
   // the preview must be stacked back at top.
   void MaybeStackPreviewAtTop();
 
   content::WebContents* preview_web_contents() const {
     return preview_web_contents_;
   }
 
-  // Sets the active top margin.
+  int preview_height() const {
+    return preview_ ? preview_->bounds().height() : 0;
+  }
+
+  // Sets the active top margin; the active WebView's y origin would be
+  // positioned at this |margin|, causing the active WebView to be pushed down
+  // vertically by |margin| pixels in the |ContentsContainer|.
   void SetActiveTopMargin(int margin);
 
   // Returns the bounds the preview would be shown at.
   gfx::Rect GetPreviewBounds() const;
 
   // Returns true if preview occupies full height of content page.
   bool IsPreviewFullHeight(int preview_height,
                            InstantSizeUnits preview_height_units) const;
 
  private:
@@ skipping 19 matching lines @@
   int active_top_margin_;
 
   // The desired height of the preview and units.
   int preview_height_;
   InstantSizeUnits preview_height_units_;
 
   DISALLOW_COPY_AND_ASSIGN(ContentsContainer);
 };
 
 #endif  // CHROME_BROWSER_UI_VIEWS_FRAME_CONTENTS_CONTAINER_H_