Generates the DTLS identity in browser process and returns it to render process.

content/common/media/dtls_identity_messages.h

+// Copyright (c) 2013 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.
+
+// IPC messages for requesting DTLS identity.
+// Multiply-included message file, hence no include guard.
+
+#include "googleurl/src/gurl.h"
+#include "ipc/ipc_message_macros.h"
+
+#define IPC_MESSAGE_START DtlsIdentityMsgStart
+
+// Messages sent from the renderer to the browser.
+// Request a DTLS identity.
+IPC_MESSAGE_CONTROL4(DTLSIdentityMsg_RequestIdentity,
+                     int /* request_id */,
+                     GURL /* origin */,
+                     std::string /* identity_name */,
+                     std::string /* common_name */)
+// Cancel a DTLS identity request.
+IPC_MESSAGE_CONTROL1(DTLSIdentityMsg_CancelRequest,
+                     int /* request_id */)

[Ryan Sleevi, 2013/06/13 22:36:47]

Should the renderer be the one cancelling, or should the browser be tracking
when a request should be cancelled?

From a security perspective, I don't think we'd want to trust the renderer to be
responsible for cancelling or cleaning up after itself, so I'm not sure where
this IPC comes into play.

[jiayl, 2013/06/14 00:37:01]

We want to cancel the request to avoid wasting resources on unuseful tasks; so
if DTLSIdentityService is going away, it has a chance to cancel the request. The
browser does not assume that the request has to be cancelled, and it should work
fine if an obsolete request is not cancelled, except wasting some CPU cycles.  

+
+// Messages sent from the browser to the renderer.
+// Return a DTLS identity.
+IPC_MESSAGE_CONTROL3(DTLSIdentityHostMsg_IdentityReady,
+                     int /* request_id */,
+                     std::string /* certificate */,
+                     std::string /* private_key */)
+// Notifies an error from the identity request.
+IPC_MESSAGE_CONTROL2(DTLSIdentityHostMsg_RequestFailed,
+                     int /* request_id */,
+                     int /* error */)