Try --force-uninstall param to see if that fixes installer tests.

chrome/test/mini_installer_test/chrome_mini_installer.cc

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/test/mini_installer_test/chrome_mini_installer.h"
 
 #include <algorithm>
 
 #include "base/path_service.h"
 #include "base/platform_thread.h"
@@ skipping 191 matching lines @@
   printf("\n\nUninstalling Chrome...\n");
   printf("Closing Chrome processes, if any...\n");
   CloseProcesses(installer_util::kChromeExe);
   std::wstring uninstall_path = GetUninstallPath();
   if (uninstall_path == L"") {
     printf("exiting.. Not proceeding with uninstall\n");
     return;
   }
   ASSERT_TRUE(file_util::PathExists(uninstall_path));
   std::wstring uninstall_args = L"\"" + uninstall_path +
-                                L"\"" + L" -uninstall";
+                                L"\"" + L" --uninstall --force-uninstall";
   if (install_type_ == mini_installer_constants::kSystemInstall)
-    uninstall_args = uninstall_args + L" -system-level";
+    uninstall_args = uninstall_args + L" --system-level";
   base::LaunchApp(uninstall_args, false, false, NULL);
-  printf("Launched setup.exe -uninstall....\n");
-  ASSERT_TRUE(CloseUninstallWindow());
+  printf("Launched setup.exe --uninstall --force-uninstall....\n");
+  // ASSERT_TRUE(CloseUninstallWindow());
   WaitUntilProcessStopsRunning(
       mini_installer_constants::kChromeSetupExecutable);
   printf("\n\nUninstall Checks:\n\n");
   ASSERT_FALSE(CheckRegistryKeyOnUninstall(dist->GetVersionKey()));
   DeleteAppFolder();
   FindChromeShortcut();
   CloseProcesses(mini_installer_constants::kIEExecutable);
   ASSERT_EQ(0,
       base::GetProcessCount(mini_installer_constants::kIEExecutable, NULL));
 }
@@ skipping 453 matching lines @@
     while ((base::GetProcessCount(process_name, NULL) > 0) &&
            (timer < 60000)) {
       PlatformThread::Sleep(200);
       timer = timer + 200;
     }
   }
   else {
     ASSERT_EQ(0, base::GetProcessCount(process_name, NULL));
   }
 }