While screencasting a tab, do not disable rendering updates while hidden.

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 "base/basictypes.h"
 #include "base/callback_forward.h"
 #include "base/process_util.h"
@@ skipping 202 matching lines @@
   virtual uint64 GetUploadPosition() const = 0;
 
   // Return the character encoding of the page.
   virtual const std::string& GetEncoding() const = 0;
 
   // True if this is a secure page which displayed insecure content.
   virtual bool DisplayedInsecureContent() const = 0;
 
   // Internal state ------------------------------------------------------------
 
-  // This flag indicates whether the WebContents is currently being
-  // screenshotted.
-  virtual void SetCapturingContents(bool cap) = 0;
+  // Indicates whether the WebContents is being captured (e.g., for screenshots
+  // or mirroring).  Increment calls must be balanced with an equivalent number
+  // of decrement calls.
+  virtual void IncrementCapturerCount() = 0;
+  virtual void DecrementCapturerCount() = 0;
 
   // Indicates whether this tab should be considered crashed. The setter will
   // also notify the delegate when the flag is changed.
   virtual bool IsCrashed() const  = 0;
   virtual void SetIsCrashed(base::TerminationStatus status, int error_code) = 0;
 
   virtual base::TerminationStatus GetCrashedStatus() const = 0;
 
   // Whether the tab is in the process of being destroyed.
   virtual bool IsBeingDestroyed() const = 0;
@@ skipping 198 matching lines @@
   // is not resized to the given image_size. If 0 is passed, the first frame of
   // the image is returned.
   virtual int DownloadFavicon(const GURL& url, int image_size,
                               const FaviconDownloadCallback& callback) = 0;
 
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_