Fix temp dir cleanup in some media unit_tests.

ScopedTempDirs must outlive anything that holds file(s) open within
them; otherwise, they are unable to delete their backing directories.

BUG=546640


Change-Id: I9a47962d2f4fae44da1882d25383af6b6b3839a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1893274
Auto-Submit: Greg Thompson <grt@chromium.org>
Commit-Queue: Tommi <tommi@chromium.org>
Reviewed-by: Tommi <tommi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711230}

chrome/browser/media/history/media_history_store_unittest.cc

@@ -46,6 +46,9 @@ class MediaHistoryStoreUnitTest : public testing::Test {
     EXPECT_TRUE(db_.Open(db_file));
   }
 
+ private:
+  base::ScopedTempDir temp_dir_;
+
  protected:
   sql::Database& GetDB() { return db_; }
   content::BrowserTaskEnvironment task_environment_;
@@ -53,7 +56,6 @@ class MediaHistoryStoreUnitTest : public testing::Test {
  private:
   sql::Database db_;
   std::unique_ptr<MediaHistoryStore> media_history_store_;
-  base::ScopedTempDir temp_dir_;
 };
 
 TEST_F(MediaHistoryStoreUnitTest, CreateDatabaseTables) {

chrome/browser/media/media_engagement_service_unittest.cc

@@ -278,12 +278,12 @@ class MediaEngagementServiceTest : public ChromeRenderViewHostTestHarness,
   scoped_refptr<base::TestMockTimeTaskRunner> mock_time_task_runner_;
 
  private:
+  base::ScopedTempDir temp_dir_;
+
   base::SimpleTestClock test_clock_;
 
   std::unique_ptr<MediaEngagementService> service_;
 
-  base::ScopedTempDir temp_dir_;
-
   base::test::ScopedFeatureList scoped_feature_list_;
 };