Fire visibilityChange event on out-of-process iframes.

content/common/page_messages.h

Index: content/common/page_messages.h
diff --git a/content/common/page_messages.h b/content/common/page_messages.h
index afe62b8a24acd99de70faca9f017abdcf5b97603..77aa978ce9c5e976b42230ad23d81015db7e01b5 100644
--- a/content/common/page_messages.h
+++ b/content/common/page_messages.h
@@ -27,6 +27,12 @@ IPC_MESSAGE_ROUTED2(PageMsg_SetZoomLevel,
                     PageMsg_SetZoomLevel_Command /* command */,
                     double /* zoom_level */)
 
+// Informs the renderer that the page was hidden.
+IPC_MESSAGE_ROUTED0(PageMsg_WasHidden)
+
+// Informs the renderer that the page is no longer hidden.
+IPC_MESSAGE_ROUTED0(PageMsg_WasShown)
+
 // -----------------------------------------------------------------------------
 // Messages sent from the renderer to the browser.