Remove keep-alive impulse IPCs from NaCl modules.

ppapi/shared_impl/ppapi_constants.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PPAPI_SHARED_IMPL_PPAPI_CONSTANTS_H_
 #define PPAPI_SHARED_IMPL_PPAPI_CONSTANTS_H_
 
 #include "build/build_config.h"
 #include "ppapi/shared_impl/ppapi_shared_export.h"
 
 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)
 const char kPowerSaverTestPluginName[] = "power_saver_test_plugin.plugin";
 #elif defined(OS_POSIX)
 const char kPowerSaverTestPluginName[] = "libpower_saver_test_plugin.so";
 #endif
 
 // Name of the root directory in the plugin private file system.
 const char kPluginPrivateRootName[] = "pluginprivate";
 
 }  // namespace ppapi
 
 #endif  // PPAPI_SHARED_IMPL_PPAPI_CONSTANTS_H_