Remove utility process batch mode support and its IPCs

The utility_process_host_impl batch mode feature has no users
anymore, nor is it a useful feature in the age of mojo. Ditch
the feature:

  - remove batch mode IPC and the message file.
  - remove StartBatchMode / EndBatchMode code.
  - change IPC unit tests to use AutomationMsgStart
    IPC start name (instead of UtilityMsgStart).
  - remove UtilityMsgStart IPC message start name.
  - utility_process_host_impl.*, document members
    and remove old / unused #include files.
  - utility_thread{,impl}.h, ditto.

No change in behavior, no new tests.

Bug: 738648
Change-Id: Ifcb65939ba7bf0a52451d2b8cb3a8a254399fcd2
Reviewed-on: https://chromium-review.googlesource.com/558526
Commit-Queue: Noel Gordon <[email protected]>
Reviewed-by: John Abd-El-Malek <[email protected]>
Reviewed-by: Ken Rockot <[email protected]>
Reviewed-by: Robert Sesek <[email protected]>
Reviewed-by: Sam McNally <[email protected]>
Cr-Commit-Position: refs/heads/master@{#484557}
diff --git a/ipc/ipc_channel_proxy_unittest_messages.h b/ipc/ipc_channel_proxy_unittest_messages.h
index 288ce53..ae45059 100644
--- a/ipc/ipc_channel_proxy_unittest_messages.h
+++ b/ipc/ipc_channel_proxy_unittest_messages.h
@@ -30,15 +30,15 @@
 
 #endif  // IPC_CHANNEL_PROXY_UNITTEST_MESSAGES_H_
 
-
+#undef IPC_MESSAGE_START
 #define IPC_MESSAGE_START TestMsgStart
 IPC_MESSAGE_CONTROL0(TestMsg_Bounce)
 IPC_MESSAGE_CONTROL0(TestMsg_SendBadMessage)
 IPC_MESSAGE_CONTROL1(TestMsg_BadMessage, BadType)
 
 #undef IPC_MESSAGE_START
-#define IPC_MESSAGE_START UtilityMsgStart
-IPC_MESSAGE_CONTROL0(UtilityMsg_Bounce)
+#define IPC_MESSAGE_START AutomationMsgStart
+IPC_MESSAGE_CONTROL0(AutomationMsg_Bounce)
 
 #undef IPC_MESSAGE_START
 #define IPC_MESSAGE_START WorkerMsgStart