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

chrome/test/mini_installer_test/chrome_mini_installer.cc

Index: chrome/test/mini_installer_test/chrome_mini_installer.cc
diff --git a/chrome/test/mini_installer_test/chrome_mini_installer.cc b/chrome/test/mini_installer_test/chrome_mini_installer.cc
index 93bdf3d2c04eb59f4a4e63bd48073b727e9ba1ca..0da0b76bcac67ce206999ecefee3d6ba68088048 100644
--- a/chrome/test/mini_installer_test/chrome_mini_installer.cc
+++ b/chrome/test/mini_installer_test/chrome_mini_installer.cc
@@ -209,12 +209,12 @@ void ChromeMiniInstaller::UnInstall() {
   }
   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");