Improve error handling in the process library.

runtime/bin/eventhandler_linux.cc

Index: runtime/bin/eventhandler_linux.cc
diff --git a/runtime/bin/eventhandler_linux.cc b/runtime/bin/eventhandler_linux.cc
index fded12e5cc818ea0855bae7743b6686dc2f86d50..a72f42a36ed6794f39ba5208ff642246e2e72e5a 100644
--- a/runtime/bin/eventhandler_linux.cc
+++ b/runtime/bin/eventhandler_linux.cc
@@ -60,7 +60,7 @@ EventHandlerImplementation::~EventHandlerImplementation() {
 void EventHandlerImplementation::SetPort(intptr_t fd,
                                          Dart_Port dart_port,
                                          intptr_t mask) {
-  assert(fd >= 0);
+  ASSERT(fd >= 0);
   if (fd >= port_map_size_) {
     intptr_t new_port_map_size = port_map_size_;
     do {
@@ -256,7 +256,7 @@ void EventHandlerImplementation::HandleEvents(struct pollfd* pollfds,
       if (event_mask != 0) {
         intptr_t fd = pollfds[i].fd;
         Dart_Port port = PortFor(fd);
-        assert(port != 0);
+        ASSERT(port != 0);
         UnregisterFd(fd);
         Dart_PostIntArray(port, 1, &event_mask);
       }