Apply modernize-make-unique for ChromeOS

This picks up make_unique changes for target_os = "chromeos" which were
not hit on my previous Mac build.

This is a large-scale change: go/chromium-modernize-make-unique

Bug: 1194272
Change-Id: Ia5c355daecbcb0c81d69db746c97c9f321b22bae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2826514
Commit-Queue: Peter Boström <pbos@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Owners-Override: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#872701}

diff --git a/chromeos/process_proxy/process_output_watcher_unittest.cc b/chromeos/process_proxy/process_output_watcher_unittest.cc
index 9db4cd1..a5ad705 100644
--- a/chromeos/process_proxy/process_output_watcher_unittest.cc
+++ b/chromeos/process_proxy/process_output_watcher_unittest.cc

@@ -145,7 +145,8 @@
 
   void RunTest(const std::vector<TestCase>& test_cases) {
     ASSERT_FALSE(output_watch_thread_started_);
-    output_watch_thread_.reset(new base::Thread("ProcessOutpuWatchThread"));
+    output_watch_thread_ =
+        std::make_unique<base::Thread>("ProcessOutpuWatchThread");
     output_watch_thread_started_ = output_watch_thread_->StartWithOptions(
         base::Thread::Options(base::MessagePumpType::IO, 0));
     ASSERT_TRUE(output_watch_thread_started_);