Simplify BrowserContext by removing redundant methods.

extensions/browser/api_unittest.cc

Index: extensions/browser/api_unittest.cc
diff --git a/extensions/browser/api_unittest.cc b/extensions/browser/api_unittest.cc
index ada00c015061d937c2ee0f9c75e44e5edfbc5fde..2ca5e16fa23c1104ef035387d4d4e784bfa5b387 100644
--- a/extensions/browser/api_unittest.cc
+++ b/extensions/browser/api_unittest.cc
@@ -53,6 +53,12 @@ void ApiUnitTest::SetUp() {
                    .Build();
 }
 
+void ApiUnitTest::TearDown() {
+  extension_ = nullptr;
+  contents_.reset();
+  ExtensionsTest::TearDown();
+}
+
 void ApiUnitTest::CreateBackgroundPage() {
   if (!contents_) {
     GURL url = BackgroundInfo::GetBackgroundURL(extension());