ipc: Create an unforgeable mechanism to get the process id of the sender.

ChannelReader now adds the process id of the sender to all external messages.

BUG=513431

Review URL: https://codereview.chromium.org/1262543003

Cr-Commit-Position: refs/heads/master@{#340798}


CrOS-Libchrome-Original-Commit: 3c175a3dbe6f597c6011975d7488e5db8283760c
diff --git a/ipc/attachment_broker_messages.h b/ipc/attachment_broker_messages.h
index 71b8986..066e19c 100644
--- a/ipc/attachment_broker_messages.h
+++ b/ipc/attachment_broker_messages.h
@@ -51,10 +51,7 @@
 // Sent from a non-broker to a broker to request the duplication of a HANDLE
 // into a different process (possibly the broker process, or even the original
 // process).
-// TODO(erikchen): https://code.google.com/p/chromium/issues/detail?id=513431
-// *sender_pid* should be unforgeably generated by the receiving channel.
-IPC_MESSAGE_CONTROL2(
+IPC_MESSAGE_CONTROL1(
     AttachmentBrokerMsg_DuplicateWinHandle,
-    IPC::internal::HandleAttachmentWin::WireFormat /* wire_format */,
-    base::ProcessId /* sender_pid */)
+    IPC::internal::HandleAttachmentWin::WireFormat /* wire_format */)
 #endif  // defined(OS_WIN)