[Blimp] Refactor Blimp test engine with embedded test server and URL rewriting

blimp/engine/testing/app/content_testing_main.cc

+// Copyright (c) 2016 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 "blimp/engine/testing/app/content_testing_main.h"
+
+#include <iostream>
+#include <memory>
+
+#include "base/logging.h"
+#include "blimp/engine/testing/app/blimp_url_rewriter.h"
+#include "blimp/engine/testing/session/blimp_engine_testing_session.h"
+#include "content/browser/browser_url_handler_impl.h"
+#include "content/public/app/content_main_runner.h"
+#include "content/public/browser/browser_url_handler.h"
+#include "net/test/embedded_test_server/embedded_test_server.h"
+
+namespace blimp {
+namespace engine {
+
+namespace test {
+
+const base::FilePath::CharType kBlimpTestRoot[] = FILE_PATH_LITERAL("");
+
+int ContentTestingMain(const content::ContentMainParams& params) {
+  std::unique_ptr<content::ContentMainRunner> main_runner(
+      content::ContentMainRunner::Create());
+
+  int exit_code = main_runner->Initialize(params);
+
+  blimp::engine::test::g_ets_instance.reset(new net::EmbeddedTestServer());
+  blimp::engine::test::g_ets_instance->ServeFilesFromSourceDirectory(
+      base::FilePath(kBlimpTestRoot));
+  DCHECK(blimp::engine::test::g_ets_instance->Start());

[shenghuazhang, 2016/12/13 02:14:19]

main_runner->Run() complains that Zygote should be the single thread, while
embedded test server is considered as another thread, so RunZygote()() failed.

Error message: https://paste.googleplex.com/6451644472492032

I think we could do this by inserting the code of starting the ets instance
after the ZygoteMain() in the main_runner->Run() process, possibly place is:

https://codesearch.chromium.org/chromium/src/content/app/content_main_runner....

But I think that costs much to override the serial of content runner classes to
reach that. 

[jbudorick, 2016/12/13 18:31:03]

We would definitely need to start the ETS instance after we spawn the zygote.
What about doing something w/ BrowserMainParts?

+
+  content::BrowserURLHandler::GetInstance()->AddHandlerPair(
+      &blimp::engine::test::HandleBlimpTestURL,
+      content::BrowserURLHandler::null_handler());
+
+  if (exit_code >= 0)
+    return exit_code;
+
+  exit_code = main_runner->Run();
+
+  main_runner->Shutdown();
+
+  DCHECK(blimp::engine::test::g_ets_instance->ShutdownAndWaitUntilComplete());
+
+  return exit_code;
+}
+
+}  // namespace test
+
+}  // namespace engine
+}  // namespace blimp