Extract ResultCatcher from ExtensionApiTest. Use it in ShellApiTest.

chrome/browser/extensions/api/dns/dns_apitest.cc

-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "base/memory/ref_counted.h"
-#include "chrome/browser/extensions/extension_apitest.h"
-#include "extensions/browser/api/dns/host_resolver_wrapper.h"
-#include "extensions/browser/api/dns/mock_host_resolver_creator.h"
-#include "net/dns/mock_host_resolver.h"
-
-class DnsApiTest : public ExtensionApiTest {
- public:
-  DnsApiTest() : resolver_creator_(new extensions::MockHostResolverCreator()) {}
-
- private:
-  virtual void SetUpOnMainThread() OVERRIDE {
-    ExtensionApiTest::SetUpOnMainThread();
-    extensions::HostResolverWrapper::GetInstance()->SetHostResolverForTesting(
-        resolver_creator_->CreateMockHostResolver());
-  }
-
-  virtual void TearDownOnMainThread() OVERRIDE {
-    extensions::HostResolverWrapper::GetInstance()->
-        SetHostResolverForTesting(NULL);
-    resolver_creator_->DeleteMockHostResolver();
-    ExtensionApiTest::TearDownOnMainThread();
-  }
-
-  // The MockHostResolver asserts that it's used on the same thread on which
-  // it's created, which is actually a stronger rule than its real counterpart.
-  // But that's fine; it's good practice.
-  scoped_refptr<extensions::MockHostResolverCreator> resolver_creator_;
-};
-
-IN_PROC_BROWSER_TEST_F(DnsApiTest, DnsExtension) {
-  ASSERT_TRUE(RunExtensionTest("dns/api")) << message_;
-}