Backport some tests in /chrome/renderer/safe_browsing to SingleThreadTaskEnvironment

These tests were previously migrated from single-threaded MessageLoop to
a multi-threaded TaskEnvironment (then named ScopedTaskEnvironment) as
part of crbug.com/891670.

//base OWNERS decided in retrospect that it was better to keep a
single-threaded option for TaskEnvironment and introduced
SingleThreadTaskEnvironment. This CL retrofits that decision for
/chrome/renderer/safe_browsing.

This CL is a no-op if it passes CQ.

This CL was uploaded by git cl split.

R=nparker@chromium.org

Bug: 891670
Change-Id: I0203844067bd2b49af1ad442973700175288930e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787177
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: Nathan Parker <nparker@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694569}

chrome/renderer/safe_browsing/phishing_term_feature_extractor_unittest.cc

@@ -131,7 +131,7 @@ class PhishingTermFeatureExtractorTest : public ::testing::Test {
     active_run_loop_->QuitWhenIdle();
   }
 
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   std::unique_ptr<base::RunLoop> active_run_loop_;
   MockFeatureExtractorClock clock_;
   std::unique_ptr<PhishingTermFeatureExtractor> extractor_;