IWYU fix in visitedlink_unittest.cc.

Also ensure that the temp dir can be deleted in TearDown.

BUG=546640
R=sky@chromium.org

Change-Id: I8e939324616a3e278c0508f639d0caaec2042f56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1894007
Commit-Queue: Scott Violet <sky@chromium.org>
Auto-Submit: Greg Thompson <grt@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#712235}

components/visitedlink/test/visitedlink_unittest.cc

@@ -12,6 +12,7 @@
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
+#include "base/files/scoped_temp_dir.h"
 #include "base/location.h"
 #include "base/macros.h"
 #include "base/process/process_handle.h"
@@ -239,7 +240,10 @@ class VisitedLinkTest : public testing::Test {
     visited_file_ = history_dir_.Append(FILE_PATH_LITERAL("VisitedLinks"));
   }
 
-  void TearDown() override { ClearDB(); }
+  void TearDown() override {
+    ClearDB();
+    ASSERT_TRUE(temp_dir_.Delete());
+  }
 
   base::ScopedTempDir temp_dir_;