Remove keep-alive impulse IPCs from NaCl modules.

ppapi/shared_impl/ppapi_constants.h

Index: ppapi/shared_impl/ppapi_constants.h
diff --git a/ppapi/shared_impl/ppapi_constants.h b/ppapi/shared_impl/ppapi_constants.h
index c26d9a7d01e482ba8c404b24daa1e39d0a43adec..6fdb00e45dc5763b6d5e6b3d23e186215f96da61 100644
--- a/ppapi/shared_impl/ppapi_constants.h
+++ b/ppapi/shared_impl/ppapi_constants.h
@@ -10,11 +10,6 @@
 
 namespace ppapi {
 
-// Default interval to space out IPC messages sent indicating that a plugin is
-// active and should be kept alive. The value must be smaller than any threshold
-// used to kill inactive plugins by the embedder host.
-const unsigned kKeepaliveThrottleIntervalDefaultMilliseconds = 5000;
-
 #if defined(OS_WIN)
 const char kPowerSaverTestPluginName[] = "power_saver_test_plugin.dll";
 #elif defined(OS_MACOSX)