Use DownloadManager to initiate downloads from PluginInstaller.

chrome/chrome_tests_unit.gypi

Index: chrome/chrome_tests_unit.gypi
diff --git a/chrome/chrome_tests_unit.gypi b/chrome/chrome_tests_unit.gypi
index 6e01edbcbb5419d95e643c84d4a329531b4848e4..a091ea9656f72333f269c1c0f141711103a5fc94 100644
--- a/chrome/chrome_tests_unit.gypi
+++ b/chrome/chrome_tests_unit.gypi
@@ -1145,6 +1145,7 @@
         'browser/password_manager/password_store_x_unittest.cc',
         'browser/performance_monitor/database_unittest.cc',
         'browser/plugins/plugin_finder_unittest.cc',
+        'browser/plugins/plugin_installer_unittest.cc',
         'browser/plugins/plugin_metadata_unittest.cc',
         'browser/plugins/plugin_prefs_unittest.cc',
         'browser/policy/cloud/cloud_policy_invalidator_unittest.cc',
@@ -2722,6 +2723,11 @@
             'browser/ui/app_list/test/fast_show_pickler_unittest.cc',
           ],
         }],
+        ['enable_plugin_installation==0', {
+          'sources!': [
+            'browser/plugins/plugin_installer_unittest.cc',
+          ],
+        }],
       ],
     },
     {