[Extensions Menu] Properly clean up the views in BrowserActionApiTest

Properly dispose of the custom views created in BrowserActionApiTest
during the tear down phase. This prevents a UAF when the view tries to
clean up after the profile is destroyed.

This was just an issue in the test, not in the wild (where views
associated with a browser will never outlive the profile).

Bug: 984654

Change-Id: Ied7dc0bd9c471fa2445b92096550adf09575043a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2042390Reviewed-by: Peter Boström <pbos@chromium.org>
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#739077}

chrome/browser/extensions/api/extension_action/browser_action_apitest.cc

@@ -113,6 +113,13 @@ class BrowserActionApiTest : public ExtensionApiTest {
     host_resolver()->AddRule("*", "127.0.0.1");
   }
 
+  void TearDownOnMainThread() override {
+    // Clean up the test util first, so that any created UI properly removes
+    // itself before profile destruction.
+    browser_action_test_util_ = nullptr;
+    ExtensionApiTest::TearDownOnMainThread();
+  }
+
  protected:
   ExtensionActionTestHelper* GetBrowserActionsBar() {
     if (!browser_action_test_util_)