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

content/browser/web_contents/web_contents_impl.h

Index: content/browser/web_contents/web_contents_impl.h
diff --git a/content/browser/web_contents/web_contents_impl.h b/content/browser/web_contents/web_contents_impl.h
index b25ff17f9546f91629ae16a7ae4cb60bf67905d2..b3c34618728dc8d945868488555899ce1d84d96a 100644
--- a/content/browser/web_contents/web_contents_impl.h
+++ b/content/browser/web_contents/web_contents_impl.h
@@ -215,7 +215,8 @@ class CONTENT_EXPORT WebContentsImpl
   virtual uint64 GetUploadPosition() const OVERRIDE;
   virtual const std::string& GetEncoding() const OVERRIDE;
   virtual bool DisplayedInsecureContent() const OVERRIDE;
-  virtual void SetCapturingContents(bool cap) OVERRIDE;
+  virtual void IncrementCapturerCount() OVERRIDE;
+  virtual void DecrementCapturerCount() OVERRIDE;
   virtual bool IsCrashed() const OVERRIDE;
   virtual void SetIsCrashed(base::TerminationStatus status,
                             int error_code) OVERRIDE;
@@ -784,8 +785,10 @@ class CONTENT_EXPORT WebContentsImpl
 
   // Data for misc internal state ----------------------------------------------
 
-  // Whether the WebContents is currently being screenshotted.
-  bool capturing_contents_;
+  // When > 0, the WebContents is currently being captured (e.g., for
+  // screenshots or mirroring); and the underlying RenderWidgetHost should not
+  // be told it is hidden.
+  int capturer_count_;
 
   // See getter above.
   bool is_being_destroyed_;