New tabCapture.captureOffscreenTab API, initially for Presentation API 1UA mode

chrome/browser/extensions/api/tab_capture/offscreen_presentation.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 CHROME_BROWSER_EXTENSIONS_API_TAB_CAPTURE_OFFSCREEN_PRESENTATION_H_
 #define CHROME_BROWSER_EXTENSIONS_API_TAB_CAPTURE_OFFSCREEN_PRESENTATION_H_
 
 #include <string>
 #include <vector>
 
 #include "base/memory/scoped_vector.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "content/public/browser/web_contents_delegate.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 #include "ui/gfx/geometry/size.h"
 
 class Profile;
 
 namespace extensions {
 
+// TODO(miu): This file and classes should be renamed, as this implementation
+// has expanded in scope to be used for all off-screen tabs.
+
 class OffscreenPresentation;  // Forward declaration.  See below.
 
 // Creates, owns, and manages all OffscreenPresentation instances created by the
 // same extension background page.  When the extension background page's
 // WebContents is about to be destroyed, its associated
 // OffscreenPresentationsOwner and all of its OffscreenPresentation instances
 // are destroyed.
 //
 // Usage:
 //
@@ skipping 178 matching lines @@
   // This is false until after the Start() method is called, and capture of the
   // |presentation_web_contents_| is first detected.
   bool content_capture_was_detected_;
 
   DISALLOW_COPY_AND_ASSIGN(OffscreenPresentation);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_TAB_CAPTURE_OFFSCREEN_PRESENTATION_H_