Replace --ppapi-keep-alive-throttle command line switch with IPC parameter.

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
new file mode 100644
index 0000000000000000000000000000000000000000..dcc9b29de5ec06bf8c7009e301e0f13bcde75b9f
--- /dev/null
+++ b/ppapi/shared_impl/ppapi_constants.h
@@ -0,0 +1,19 @@
+// 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 "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;
+
+}  // namespace ppapi
+
+#endif  // PPAPI_SHARED_IMPL_PPAPI_CONSTANTS_H_