[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 423 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, 2017/06/10 00:53:37]

I think there's probably a better way to check this.  Ken, do you know?

[kenrb, 2017/06/12 15:26:22]

The call site should be able to use:
navigation_handle->GetWebContents()->GetTopLevelRenderWidgetHostView()->IsShowing();

[nasko, 2017/06/12 23:22:02]

Doesn't that distribute implementation logic outside of WebContents? Is there a
downside to wrapping this call into a "IsShowing()" method on the WebContents
itself?

[Zhen Wang, 2017/06/13 23:33:21]

This is one option for us to know if a tab is visible. Since TabManager is also
observing TabStripModel, we can also track tab strip events explicitly.

But I think it is better to ask WebContents for this information directly. I
thought IsVisible() or IsShowing() would be some property WebContents should
provide. Is there any downside of adding this? 

By the way, is |should_normally_be_visible_| the same as
GetTopLevelRenderWidgetHostView()->IsShowing()?

[nasko, 2017/06/15 20:01:58]

I defer to kenrb@ on this one.

[kenrb, 2017/06/15 20:53:08]

Adding that method might make sense here. The only divergence between
should_normally_be_visible_ and RWHV::IsShowing(), as far as I am aware, is that
IsShowing() will return false while a top-level page is still loading, even
though should_normally_be_visible_ might return true. Given what you are using
it for, the latter seems like it is more relevant.

[Zhen Wang, 2017/06/19 23:00:12]

Right. We will need to know if it is visible before loading. For here, I will
keep the name |IsVisible()|, so to distinguish from the |IsShown()|. Let me know
if any new name is better.

+
   // 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 368 matching lines @@
 
  private:
   // This interface should only be implemented inside content.
   friend class WebContentsImpl;
   WebContents() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_