[scheduling] Use ScopedTaskEnvironment instead of MessageLoop in image_fetcher

MessageLoop will go away, eventually.

BUG=891670

Change-Id: I9d8c29ddf02aee41b2c2f706dca49b60763ea0a2
Reviewed-on: https://chromium-review.googlesource.com/c/1353883Reviewed-by: Filip Gorski <fgorski@chromium.org>
Commit-Queue: Carlos Caballero <carlscab@google.com>
Cr-Commit-Position: refs/heads/master@{#612447}

components/image_fetcher/core/image_data_fetcher_unittest.cc

@@ -9,8 +9,9 @@
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
-#include "base/message_loop/message_loop.h"
+#include "base/run_loop.h"
 #include "base/test/bind_test_util.h"
+#include "base/test/scoped_task_environment.h"
 #include "net/base/load_flags.h"
 #include "net/http/http_response_headers.h"
 #include "net/http/http_status_code.h"
@@ -51,7 +52,7 @@ class ImageDataFetcherTest : public testing::Test {
                void(const std::string&, const RequestMetadata&));
 
  protected:
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment task_environment_;
 
   network::TestURLLoaderFactory test_url_loader_factory_;
   scoped_refptr<network::SharedURLLoaderFactory> shared_factory_;