Show more different NaCl loading errors.

ppapi/native_client/src/trusted/plugin/service_runtime.cc

Index: ppapi/native_client/src/trusted/plugin/service_runtime.cc
===================================================================
--- ppapi/native_client/src/trusted/plugin/service_runtime.cc	(revision 210749)
+++ ppapi/native_client/src/trusted/plugin/service_runtime.cc	(working copy)
@@ -734,17 +734,23 @@
                           "ServiceRuntime: failed to create sel_ldr launcher");
     return false;
   }
+  nacl::string error_message;
   bool started = tmp_subprocess->Start(plugin_->pp_instance(),
                                        url.c_str(),
                                        uses_irt,
                                        uses_ppapi,
                                        enable_ppapi_dev,
                                        enable_dyncode_syscalls,
-                                       enable_exception_handling);
+                                       enable_exception_handling,
+                                       &error_message);
   if (!started) {
     NaClLog(LOG_ERROR, "ServiceRuntime::Start (start failed)\n");
-    error_info->SetReport(ERROR_SEL_LDR_LAUNCH,
-                          "ServiceRuntime: failed to start");
+    if (error_message.empty()) {
+      error_info->SetReport(ERROR_SEL_LDR_LAUNCH,
+                            "ServiceRuntime: failed to start");
+    } else {
+      error_info->SetReport(ERROR_SEL_LDR_LAUNCH, error_message);
+    }
     return false;
   }