Reset overscroll state when OverscrollWindowDelegate is destroyed.

content/browser/web_contents/aura/overscroll_window_delegate.h

 // Copyright 2015 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 CONTENT_BROWSER_WEB_CONTENTS_AURA_OVERSCROLL_WINDOW_DELEGATE_H_
 #define CONTENT_BROWSER_WEB_CONTENTS_AURA_OVERSCROLL_WINDOW_DELEGATE_H_
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "content/browser/renderer_host/overscroll_controller.h"
@@ skipping 32 matching lines @@
   // Overridden from ui::EventHandler.
   void OnKeyEvent(ui::KeyEvent* event) override;
   void OnMouseEvent(ui::MouseEvent* event) override;
   void OnScrollEvent(ui::ScrollEvent* event) override;
   void OnGestureEvent(ui::GestureEvent* event) override;
 
   // Delegate to which we forward overscroll events.
   OverscrollControllerDelegate* delegate_;
 
   // The current overscroll mode.
-  OverscrollMode overscroll_mode_;
+  OverscrollMode overscroll_mode_ = OVERSCROLL_NONE;
 
   // The current overscroll source.
-  OverscrollSource overscroll_source_;
+  OverscrollSource overscroll_source_ = OverscrollSource::NONE;
 
   // The latest delta_x scroll update.
-  float delta_x_;
+  float delta_x_ = 0.f;
 
   // The ratio of overscroll at which we consider the overscroll completed.
   const float complete_threshold_ratio_;
 
   // The threshold for starting the overscroll gesture, for touchscreen or
   // touchpads.
   const float start_threshold_touchscreen_;
   const float start_threshold_touchpad_;
 
   // The threshold for starting the overscroll gesture for the current touch
   // input.
-  float active_start_threshold_;
+  float active_start_threshold_ = 0.f;
 
   DISALLOW_COPY_AND_ASSIGN(OverscrollWindowDelegate);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_WEB_CONTENTS_AURA_OVERSCROLL_WINDOW_DELEGATE_H_