[ios] Creates WebSubThread to mirror BrowserProcessSubThread.

Moves IO thread-specific initialization into WebSubThread.

BUG=826465

Change-Id: I5527dafdf75c29fbc8478f7500c20a96410ad008
Reviewed-on: https://chromium-review.googlesource.com/c/1335961Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Rohit Rao <rohitrao@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608898}

ios/web/BUILD.gn

@@ -71,6 +71,8 @@ source_set("web") {
     "url_util.cc",
     "web_client.mm",
     "web_kit_constants.cc",
+    "web_sub_thread.cc",
+    "web_sub_thread.h",
     "web_thread_impl.cc",
     "web_thread_impl.h",
     "web_view_creation_util.mm",

ios/web/app/web_main_loop.h

@@ -21,6 +21,7 @@ class CookieNotificationBridge;
 class ServiceManagerContext;
 class WebMainParts;
 class WebThreadImpl;
+class WebSubThread;
 
 // Implements the main web loop stages called from WebMainRunner.
 // See comments in web_main_parts.h for additional info.
@@ -83,7 +84,7 @@ class WebMainLoop {
   std::unique_ptr<WebThreadImpl> main_thread_;
 
   // Members initialized in |RunMainMessageLoopParts()| ------------------------
-  std::unique_ptr<WebThreadImpl> io_thread_;
+  std::unique_ptr<WebSubThread> io_thread_;
 
   // Members initialized in |WebThreadsStarted()| --------------------------
   std::unique_ptr<CookieNotificationBridge> cookie_notification_bridge_;

ios/web/app/web_main_loop.mm

@@ -27,6 +27,7 @@
 #import "ios/web/public/web_client.h"
 #include "ios/web/public/web_task_traits.h"
 #include "ios/web/service_manager_context.h"
+#include "ios/web/web_sub_thread.h"
 #include "ios/web/web_thread_impl.h"
 #include "ios/web/webui/url_data_manager_ios.h"
 
@@ -128,7 +129,7 @@ int WebMainLoop::CreateThreads(
 
   base::Thread::Options io_message_loop_options;
   io_message_loop_options.message_loop_type = base::MessageLoop::TYPE_IO;
-  io_thread_ = std::make_unique<WebThreadImpl>(WebThread::IO);
+  io_thread_ = std::make_unique<WebSubThread>(WebThread::IO);
   io_thread_->StartWithOptions(io_message_loop_options);
 
   // Only start IO thread above as this is the only WebThread besides UI (which

ios/web/web_sub_thread.cc

+// Copyright 2018 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 "ios/web/web_sub_thread.h"
+
+#include "base/threading/thread_restrictions.h"
+#include "ios/web/public/web_thread.h"
+#include "ios/web/web_thread_impl.h"
+#include "net/url_request/url_fetcher.h"
+
+namespace web {
+
+WebSubThread::WebSubThread(WebThread::ID identifier)
+    : WebThreadImpl(identifier) {}
+
+WebSubThread::WebSubThread(WebThread::ID identifier,
+                           base::MessageLoop* message_loop)
+    : WebThreadImpl(identifier, message_loop) {}
+
+WebSubThread::~WebSubThread() {
+  Stop();
+}
+
+void WebSubThread::Init() {
+  WebThreadImpl::Init();
+
+  if (WebThread::CurrentlyOn(WebThread::IO)) {
+    // Though this thread is called the "IO" thread, it actually just routes
+    // messages around; it shouldn't be allowed to perform any blocking disk
+    // I/O.
+    base::DisallowUnresponsiveTasks();
+  }
+}
+
+void WebSubThread::CleanUp() {
+  if (WebThread::CurrentlyOn(WebThread::IO))
+    IOThreadPreCleanUp();
+
+  WebThreadImpl::CleanUp();
+}
+
+void WebSubThread::IOThreadPreCleanUp() {
+  // Kill all things that might be holding onto
+  // net::URLRequest/net::URLRequestContexts.
+
+  // Destroy all URLRequests started by URLFetchers.
+  net::URLFetcher::CancelAll();
+}
+
+}  // namespace web

ios/web/web_sub_thread.h

+// Copyright 2018 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.
+
+#ifndef IOS_WEB_WEB_SUB_THREAD_H_
+#define IOS_WEB_WEB_SUB_THREAD_H_
+
+#include "base/macros.h"
+#include "ios/web/web_thread_impl.h"
+
+namespace web {
+
+// This simple thread object is used for the specialized threads that are spun
+// up during startup.
+class WebSubThread : public WebThreadImpl {
+ public:
+  explicit WebSubThread(WebThread::ID identifier);
+  WebSubThread(WebThread::ID identifier, base::MessageLoop* message_loop);
+  ~WebSubThread() override;
+
+ protected:
+  void Init() override;
+  void CleanUp() override;
+
+ private:
+  // These methods encapsulate cleanup that needs to happen on the IO thread
+  // before the embedder's |CleanUp()| function is called.
+  void IOThreadPreCleanUp();
+
+  DISALLOW_COPY_AND_ASSIGN(WebSubThread);
+};
+
+}  // namespace web
+
+#endif  // IOS_WEB_WEB_SUB_THREAD_H_

ios/web/web_thread_impl.cc

@@ -17,10 +17,8 @@
 #include "base/single_thread_task_runner.h"
 #include "base/task/post_task.h"
 #include "base/task/task_executor.h"
-#include "base/threading/thread_restrictions.h"
 #include "ios/web/public/web_task_traits.h"
 #include "ios/web/public/web_thread_delegate.h"
-#include "net/url_request/url_fetcher.h"
 
 namespace web {
 
@@ -223,11 +221,6 @@ void WebThreadImpl::Init() {
         base::subtle::NoBarrier_Load(&globals.io_thread_delegate);
     if (delegate)
       reinterpret_cast<WebThreadDelegate*>(delegate)->Init();
-
-    // Though this thread is called the "IO" thread, it actually just routes
-    // messages around; it shouldn't be allowed to perform any blocking disk
-    // I/O.
-    base::DisallowUnresponsiveTasks();
   }
 }
 
@@ -262,8 +255,6 @@ void WebThreadImpl::Run(base::RunLoop* run_loop) {
 
 void WebThreadImpl::CleanUp() {
   if (identifier_ == WebThread::IO) {
-    IOThreadPreCleanUp();
-
     WebThreadGlobals& globals = g_globals.Get();
     WebThreadDelegateAtomicPtr delegate =
         base::subtle::NoBarrier_Load(&globals.io_thread_delegate);
@@ -281,14 +272,6 @@ void WebThreadImpl::Initialize() {
   globals.threads[identifier_] = this;
 }
 
-void WebThreadImpl::IOThreadPreCleanUp() {
-  // Kill all things that might be holding onto
-  // net::URLRequest/net::URLRequestContexts.
-
-  // Destroy all URLRequests started by URLFetchers.
-  net::URLFetcher::CancelAll();
-}
-
 WebThreadImpl::~WebThreadImpl() {
   // All Thread subclasses must call Stop() in the destructor. This is
   // doubly important here as various bits of code check they are on

ios/web/web_thread_impl.h

@@ -51,10 +51,6 @@ class WebThreadImpl : public WebThread, public base::Thread {
   // Common initialization code for the constructors.
   void Initialize();
 
-  // Performs cleanup that needs to happen on the IO thread before calling the
-  // embedder's CleanUp function.
-  void IOThreadPreCleanUp();
-
   // For testing.
   friend class TestWebThreadBundle;
   friend class TestWebThreadBundleImpl;