[TooManyTabs] Add TabNavigationThrottle

content/public/browser/web_contents.h

 // 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.
 
 #ifndef CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 424 matching lines @@
   virtual base::TimeTicks GetLastActiveTime() const = 0;
   virtual void SetLastActiveTime(base::TimeTicks last_active_time) = 0;
 
   // Get the last time that the WebContents was made hidden.
   virtual base::TimeTicks GetLastHiddenTime() const = 0;
 
   // Invoked when the WebContents becomes shown/hidden.
   virtual void WasShown() = 0;
   virtual void WasHidden() = 0;
 
+  // Whether the WebContents is visible.
+  virtual bool IsVisible() const = 0;

[Charlie Reis, 2017/07/06 23:50:31]

I still find this confusing vs RWHV::IsShowing(), since both the name and
implementation are subtly different.  Can you update the comment to say how this
differs from RenderWidgetHostView::IsShowing() (i.e., returns true even before
the page loads)?

[Zhen Wang, 2017/07/07 18:06:39]

Added comments now. Ken, can you double check if this makes sense? Thanks!

+
   // Returns true if the before unload and unload listeners need to be
   // fired. The value of this changes over time. For example, if true and the
   // before unload listener is executed and allows the user to exit, then this
   // returns false.
   virtual bool NeedToFireBeforeUnload() = 0;
 
   // Runs the beforeunload handler for the main frame. See also ClosePage and
   // SwapOut in RenderViewHost, which run the unload handler.
   //
   // TODO(creis): We should run the beforeunload handler for every frame that
@@ skipping 383 matching lines @@
 
  private:
   // This interface should only be implemented inside content.
   friend class WebContentsImpl;
   WebContents() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_