Expose the visibility state of a frame to the browser process.

content/public/browser/content_browser_client.h

Index: content/public/browser/content_browser_client.h
diff --git a/content/public/browser/content_browser_client.h b/content/public/browser/content_browser_client.h
index 39acf3dabc301a66708d68280659d07912da33d5..d97a87b2d427508961d2973e1f2cbb606a7a872c 100644
--- a/content/public/browser/content_browser_client.h
+++ b/content/public/browser/content_browser_client.h
@@ -28,6 +28,7 @@
 #include "net/url_request/url_request_interceptor.h"
 #include "net/url_request/url_request_job_factory.h"
 #include "storage/browser/fileapi/file_system_context.h"
+#include "third_party/WebKit/public/platform/WebPageVisibilityState.h"
 #include "ui/base/window_open_disposition.h"
 
 #if defined(OS_POSIX) && !defined(OS_MACOSX)
@@ -595,6 +596,12 @@ class CONTENT_EXPORT ContentBrowserClient {
   virtual void GetAdditionalNavigatorConnectServices(
       const scoped_refptr<NavigatorConnectContext>& context) {}
 
+  // Allows to override the visibility state of a RenderFrameHost.
+  // |visibility_state| should not be null. It will only be set if needed.
+  virtual void OverridePageVisibilityState(
+      RenderFrameHost* render_frame_host,
+      blink::WebPageVisibilityState* visibility_state) {}
+
 #if defined(OS_POSIX) && !defined(OS_MACOSX)
   // Populates |mappings| with all files that need to be mapped before launching
   // a child process.