Changing SpawnChild to return a struct.

mojo/edk/system/message_pipe_dispatcher.cc

Index: mojo/edk/system/message_pipe_dispatcher.cc
diff --git a/mojo/edk/system/message_pipe_dispatcher.cc b/mojo/edk/system/message_pipe_dispatcher.cc
index f27336b56f4d074a0e5e32ec2a592fcccff363a3..6963ec2463b33aac47c5214d7af28cf03579205d 100644
--- a/mojo/edk/system/message_pipe_dispatcher.cc
+++ b/mojo/edk/system/message_pipe_dispatcher.cc
@@ -286,8 +286,10 @@ MojoResult MessagePipeDispatcher::ReadMessage(
                            &no_space, &invalid_message);
   int rv = node_controller_->node()->GetMessage(port_, &ports_message, &filter);
 
-  if (invalid_message)
+  if (invalid_message) {
+    NOTREACHED();
     return MOJO_RESULT_UNKNOWN;
+  }
 
   if (rv != ports::OK && rv != ports::ERROR_PORT_PEER_CLOSED) {
     if (rv == ports::ERROR_PORT_UNKNOWN ||
@@ -327,8 +329,10 @@ MojoResult MessagePipeDispatcher::ReadMessage(
   const DispatcherHeader* dispatcher_headers =
       reinterpret_cast<const DispatcherHeader*>(header + 1);
 
-  if (header->num_dispatchers > std::numeric_limits<uint16_t>::max())
+  if (header->num_dispatchers > std::numeric_limits<uint16_t>::max()) {
+    NOTREACHED();
     return MOJO_RESULT_UNKNOWN;
+  }
 
   // Deserialize dispatchers.
   if (header->num_dispatchers > 0) {
@@ -336,8 +340,10 @@ MojoResult MessagePipeDispatcher::ReadMessage(
     std::vector<DispatcherInTransit> dispatchers(header->num_dispatchers);
     size_t data_payload_index = sizeof(MessageHeader) +
         header->num_dispatchers * sizeof(DispatcherHeader);
-    if (data_payload_index > header->header_size)
+    if (data_payload_index > header->header_size) {
+      NOTREACHED();
       return MOJO_RESULT_UNKNOWN;
+    }
     const char* dispatcher_data = reinterpret_cast<const char*>(
         dispatcher_headers + header->num_dispatchers);
     size_t port_index = 0;
@@ -351,17 +357,21 @@ MojoResult MessagePipeDispatcher::ReadMessage(
       size_t next_payload_index = data_payload_index + dh.num_bytes;
       if (msg->num_payload_bytes() < next_payload_index ||
           next_payload_index < data_payload_index) {
+        NOTREACHED();
         return MOJO_RESULT_UNKNOWN;
       }
 
       size_t next_port_index = port_index + dh.num_ports;
-      if (msg->num_ports() < next_port_index || next_port_index < port_index)
+      if (msg->num_ports() < next_port_index || next_port_index < port_index) {
+        NOTREACHED();
         return MOJO_RESULT_UNKNOWN;
+      }
 
       size_t next_platform_handle_index =
           platform_handle_index + dh.num_platform_handles;
       if (num_msg_handles < next_platform_handle_index ||
           next_platform_handle_index < platform_handle_index) {
+        NOTREACHED();
         return MOJO_RESULT_UNKNOWN;
       }
 
@@ -371,8 +381,10 @@ MojoResult MessagePipeDispatcher::ReadMessage(
       dispatchers[i].dispatcher = Dispatcher::Deserialize(
           type, dispatcher_data, dh.num_bytes, msg->ports() + port_index,
           dh.num_ports, out_handles, dh.num_platform_handles);
-      if (!dispatchers[i].dispatcher)
+      if (!dispatchers[i].dispatcher) {
+        NOTREACHED();
         return MOJO_RESULT_UNKNOWN;
+      }
 
       dispatcher_data += dh.num_bytes;
       data_payload_index = next_payload_index;
@@ -381,8 +393,10 @@ MojoResult MessagePipeDispatcher::ReadMessage(
     }
 
     if (!node_controller_->core()->AddDispatchersFromTransit(dispatchers,
-                                                             handles))
+                                                             handles)) {
+      NOTREACHED();
       return MOJO_RESULT_UNKNOWN;
+    }
   }
 
   CHECK(msg);