[ios] Cleanup resource bundle in WebTestSuite::Shutdown.

BUG=None

Review-Url: https://codereview.chromium.org/2037763002
Cr-Commit-Position: refs/heads/master@{#397881}

ios/web/test/web_test_suite.h

@@ -17,7 +17,9 @@ class WebTestSuite : public base::TestSuite {
   ~WebTestSuite() override;
 
  protected:
+  // base::TestSuite overrides.
   void Initialize() override;
+  void Shutdown() override;
 
  private:
   // Sets web client on construction and restores the original on destruction.

ios/web/test/web_test_suite.mm

@@ -58,4 +58,9 @@ void WebTestSuite::Initialize() {
       resources_pack_path, ui::SCALE_FACTOR_NONE);
 }
 
+void WebTestSuite::Shutdown() {
+  ResourceBundle::CleanupSharedInstance();
+  base::TestSuite::Shutdown();
+}
+
 }  // namespace web