Test Keeping NaCl plugins used in app background pages alive when active.

ppapi/shared_impl/ppapi_switches.cc

Index: ppapi/shared_impl/ppapi_switches.cc
diff --git a/ppapi/shared_impl/ppapi_switches.cc b/ppapi/shared_impl/ppapi_switches.cc
index 84ba25034ecb4a361bf4531119be68d440b14959..2a3f1c286008740104d5aaa8df81d6bf93205f95 100644
--- a/ppapi/shared_impl/ppapi_switches.cc
+++ b/ppapi/shared_impl/ppapi_switches.cc
@@ -9,4 +9,7 @@ namespace switches {
 // Enables the testing interface for PPAPI.
 const char kEnablePepperTesting[] = "enable-pepper-testing";
 
+// Specifies throttling time in milliseconds for PpapiHostMsg_Keepalive IPCs.
+const char kPpapiKeepAliveThrottle[] = "ppapi-keep-alive-throttle";
+
 }  // namespace switches