Tabs being screen-captured will fullscreen within their tab contents area.

chrome/browser/ui/browser.cc

Index: chrome/browser/ui/browser.cc
diff --git a/chrome/browser/ui/browser.cc b/chrome/browser/ui/browser.cc
index 87acf52c3f42ef8b404ee151571318bd5cbfd81b..38858828e5aafd426d309236d30dd0eb946d22eb 100644
--- a/chrome/browser/ui/browser.cc
+++ b/chrome/browser/ui/browser.cc
@@ -981,6 +981,8 @@ void Browser::ActiveTabChanged(WebContents* old_contents,
   // is updated.
   window_->OnActiveTabChanged(old_contents, new_contents, index, reason);
 
+  fullscreen_controller_->OnTabDetachedFromView(old_contents);

[sky, 2014/02/12 21:30:13]

Is it possible to make fullscreencontroller observer the TabStripModel directly?
Or are the ordering dependencies if we do that?

[miu, 2014/02/12 21:49:14]

Yes, there are definitely ordering dependencies, both for existing code and the
new code introduced in this CL.  In this CL, FullscreenController resizes a
detached fullscreen widget to the video resolution of the tab capture.  The
widget needs to be detached first (via the statement above this one) for this to
work correctly.

+
   // Discarded tabs always get reloaded.
   if (tab_strip_model_->IsTabDiscarded(index)) {
     LOG(WARNING) << "Reloading discarded tab at " << index;