Only copy the plugin if it doesn't already exist.

chrome/test/ui/npapi_test_helper.cc

 // Copyright 2008, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 // Copyright (c) 2009 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.
 
@@ skipping 27 matching lines @@
   // We need to copy our test-plugin into the plugins directory so that
   // the browser can load it.
   // TODO(tc): We should copy the plugins as a build step, not during
   // the tests.  Then we don't have to clean up after the copy in the test.
   FilePath plugins_directory = GetPluginsDirectory();
   FilePath plugin_src = browser_directory_.AppendASCII(test_plugin_name_);
   ASSERT_TRUE(file_util::PathExists(plugin_src));
   test_plugin_path_ = plugins_directory.AppendASCII(test_plugin_name_);
 
   file_util::CreateDirectory(plugins_directory);
-  ASSERT_TRUE(file_util::CopyDirectory(plugin_src, test_plugin_path_, true))
-      << "Copy failed from " << plugin_src.value()
-      << " to " << test_plugin_path_.value();
+  if (!file_util::PathExists(test_plugin_path_)) {
+    ASSERT_TRUE(file_util::CopyDirectory(plugin_src, test_plugin_path_, true))
+        << "Copy failed from " << plugin_src.value()
+        << " to " << test_plugin_path_.value();
+  }
 #if defined(OS_MACOSX)
   // The plugins directory isn't read by default on the Mac, so it needs to be
   // explicitly registered.
   launch_arguments_.AppendSwitchPath(switches::kExtraPluginDir,
                                      plugins_directory);
 #endif
 
   UITest::SetUp();
 }
 
@@ skipping 37 matching lines @@
 void NPAPIVisiblePluginTester::SetUp() {
   show_window_ = true;
   NPAPITester::SetUp();
 }
 
 // NPAPIIncognitoTester members.
 void NPAPIIncognitoTester::SetUp() {
   launch_arguments_.AppendSwitch(switches::kIncognito);
   NPAPITester::SetUp();
 }