Show more different NaCl loading errors.

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

Index: ppapi/native_client/src/trusted/plugin/sel_ldr_launcher_chrome.cc
===================================================================
--- ppapi/native_client/src/trusted/plugin/sel_ldr_launcher_chrome.cc	(revision 212679)
+++ ppapi/native_client/src/trusted/plugin/sel_ldr_launcher_chrome.cc	(working copy)
@@ -6,6 +6,8 @@
 #include "ppapi/native_client/src/trusted/plugin/nacl_entry_points.h"
 #include "ppapi/native_client/src/trusted/plugin/sel_ldr_launcher_chrome.h"
 
+#include "ppapi/cpp/var.h"
+
 LaunchNaClProcessFunc launch_nacl_process = NULL;
 
 namespace plugin {
@@ -21,9 +23,12 @@
                                  bool uses_ppapi,
                                  bool enable_ppapi_dev,
                                  bool enable_dyncode_syscalls,
-                                 bool enable_exception_handling) {
+                                 bool enable_exception_handling,
+                                 nacl::string* error_message) {
+  *error_message = "";
   if (!launch_nacl_process)
     return false;
+  PP_Var var_error_message;
   // send a synchronous message to the browser process
   if (launch_nacl_process(instance,
                           url,
@@ -32,7 +37,12 @@
                           PP_FromBool(enable_ppapi_dev),
                           PP_FromBool(enable_dyncode_syscalls),
                           PP_FromBool(enable_exception_handling),
-                          &channel_) != PP_NACL_OK) {
+                          &channel_,
+                          &var_error_message) != PP_NACL_OK) {
+    pp::Var var_error_message_cpp(pp::PASS_REF, var_error_message);
+    if (var_error_message_cpp.is_string()) {
+      *error_message = var_error_message_cpp.AsString();
+    }
     return false;
   }
   return true;