Distinguish plugin disconnections from plugin crashes.

content/common/view_messages.h

Index: content/common/view_messages.h
diff --git a/content/common/view_messages.h b/content/common/view_messages.h
index 74f3a3c2d57237e39e2e15848b8888b18ed0ff60..523db500e22d4298c594289f45b62ce8b71b5d22 100644
--- a/content/common/view_messages.h
+++ b/content/common/view_messages.h
@@ -2002,10 +2002,14 @@ IPC_MESSAGE_ROUTED4(ViewHostMsg_AddMessageToConsole,
                     int32, /* line number */
                     string16 /* source id */)
 
-// Sent by the renderer process to indicate that a plugin instance has
-// crashed.
-IPC_MESSAGE_ROUTED1(ViewHostMsg_CrashedPlugin,
-                    FilePath /* plugin_path */)
+// Sent by the renderer process to indicate that a plugin instance has crashed.
+// Note: |plugin_pid| should not be trusted. The corresponding process has
+// probably died. Moreover, the ID may have been reused by a new process. Any
+// usage other than displaying it in a prompt to the user is very likely to be
+// wrong.
+IPC_MESSAGE_ROUTED2(ViewHostMsg_CrashedPlugin,
+                    FilePath /* plugin_path */,
+                    base::ProcessId /* plugin_pid */)
 
 // Displays a box to confirm that the user wants to navigate away from the
 // page. Replies true if yes, false otherwise, the reply string is ignored,