Keep event page alive when there's some Pepper plugin on it.

content/common/frame_messages.h

Index: content/common/frame_messages.h
diff --git a/content/common/frame_messages.h b/content/common/frame_messages.h
index 70870ab2f77d9c535b4b1eb73ce07755bfa00bbd..4e261f5a953c490a4a4469a0981085848052c8de 100644
--- a/content/common/frame_messages.h
+++ b/content/common/frame_messages.h
@@ -720,6 +720,14 @@ IPC_MESSAGE_ROUTED2(FrameHostMsg_DomOperationResponse,
                     int  /* automation_id */)
 
 #if defined(ENABLE_PLUGINS)
+// Notification sent from a renderer to the browser that a Pepper plugin
+// instance is created in the DOM.
+IPC_MESSAGE_ROUTED0(FrameHostMsg_PepperInstanceCreated)
+
+// Notification sent from a renderer to the browser that a Pepper plugin
+// instance is deleted from the DOM.
+IPC_MESSAGE_ROUTED0(FrameHostMsg_PepperInstanceDeleted)
+
 // Sent to the browser when the renderer detects it is blocked on a pepper
 // plugin message for too long. This is also sent when it becomes unhung
 // (according to the value of is_hung). The browser can give the user the