ExtensionsTest: Move initialization to SetUp and avoid potential UAF.

extensions/browser/policy_check_unittest.cc

Index: extensions/browser/policy_check_unittest.cc
diff --git a/extensions/browser/policy_check_unittest.cc b/extensions/browser/policy_check_unittest.cc
index 8b8af3057d2d42c91d3265f7c6d245d8c4781fa4..7d192b4c6c833cf2bbc638087db3cbbe1e5885dd 100644
--- a/extensions/browser/policy_check_unittest.cc
+++ b/extensions/browser/policy_check_unittest.cc
@@ -66,16 +66,16 @@ class TestExtensionSystem : public MockExtensionSystem {
 
 class PolicyCheckTest : public ExtensionsTest {
  public:
-  PolicyCheckTest() {
-    // Replace the MockExtensionSystemFactory set by ExtensionsTest.
-    extensions_browser_client()->set_extension_system_factory(&factory_);
-  }
+  PolicyCheckTest() {}
 
   ~PolicyCheckTest() override {}
 
   void SetUp() override {
     ExtensionsTest::SetUp();
 
+    // Replace the MockExtensionSystemFactory set by ExtensionsTest.
+    extensions_browser_client()->set_extension_system_factory(&factory_);
+
     base::DictionaryValue manifest_dict;
     manifest_dict.SetString("name", "dummy name");
     manifest_dict.SetString("version", "1");