Specify the path to the old setup.exe in the lpApplicationName parameter to CreateProcess.

chrome/installer/mini_installer/mini_installer.cc

Index: chrome/installer/mini_installer/mini_installer.cc
diff --git a/chrome/installer/mini_installer/mini_installer.cc b/chrome/installer/mini_installer/mini_installer.cc
index da3cf91d5a6d030c98d4dab32979ddeba27c7770..e00569c7fad3d1da3206835dc2c8282ea2ee7329 100644
--- a/chrome/installer/mini_installer/mini_installer.cc
+++ b/chrome/installer/mini_installer/mini_installer.cc
@@ -405,10 +405,12 @@ bool UnpackBinaryResources(const Configuration& configuration, HMODULE module,
   // If we found setup 'B7' resource, handle it.
   if (setup_path->length() > 0) {
     CommandString cmd_line;
+    PathString exe_path;
     // Get the path to setup.exe first.
     bool success = true;
-    if (!GetSetupExePathFromRegistry(configuration, cmd_line.get(),
-                                     cmd_line.capacity()) ||
+    if (!GetSetupExePathFromRegistry(configuration, exe_path.get(),
+                                     exe_path.capacity()) ||
+        !cmd_line.append(exe_path.get()) ||
         !cmd_line.append(L" --") ||
         !cmd_line.append(kCmdUpdateSetupExe) ||
         !cmd_line.append(L"=\"") ||
@@ -429,7 +431,7 @@ bool UnpackBinaryResources(const Configuration& configuration, HMODULE module,
 
     ProcessExitCode exit_code = SUCCESS_EXIT_CODE;
     if (success &&
-        (!RunProcessAndWait(NULL, cmd_line.get(), &exit_code) ||
+        (!RunProcessAndWait(exe_path.get(), cmd_line.get(), &exit_code) ||
          exit_code != SUCCESS_EXIT_CODE)) {
       success = false;
     }