Remove references of MessageLoopForIO in /chrome/browser/android/contextualsearch

MessageLoopForIO will go away soon use ScopedTaskEnvironment instead.

ScopedTaskEnvironment will per default start a ThreadPool, which should
be fine in most of the cases. If you believe your test needs to make sure
that no ThreadPool runs let me know and I will update the patch.

BUG=891670
This CL was uploaded by git cl split.

R=donnd@chromium.org

Change-Id: Iffa04b1db906d1a04a73529a01711aa782a11971
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1733597
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: Donn Denman <donnd@chromium.org>
Commit-Queue: Donn Denman <donnd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683632}

chrome/browser/android/contextualsearch/contextual_search_delegate_unittest.cc

@@ -14,8 +14,8 @@
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/macros.h"
-#include "base/message_loop/message_loop.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/values.h"
 #include "chrome/browser/android/contextualsearch/contextual_search_context.h"
 #include "chrome/browser/android/contextualsearch/resolved_search_term.h"
@@ -288,7 +288,8 @@ class ContextualSearchDelegateTest : public testing::Test {
   std::string search_url_preload_;
   int coca_card_tag_;
 
-  base::MessageLoopForIO io_message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_{
+      base::test::ScopedTaskEnvironment::MainThreadType::IO};
   std::unique_ptr<TemplateURLService> template_url_service_;
   scoped_refptr<network::SharedURLLoaderFactory>
       test_shared_url_loader_factory_;