base: Use std::move() instead of Pass() for real movable types.

Some of our movable types have real move-constructors/assignment
operators now. We can use std::move() for these types instead of Pass().

There's still some move-only types that are implemented using an
"Rvalue" type emulation, so we have to keep Pass() for those still.

R=thestig@chromium.org
BUG=557422

Review URL: https://codereview.chromium.org/1479473002

Cr-Commit-Position: refs/heads/master@{#361583}


CrOS-Libchrome-Original-Commit: 0c8d4aa8ba54f463cc22ce21bf1088edd3d1e207
diff --git a/base/files/file_path_watcher.h b/base/files/file_path_watcher.h
index 4f132af..834acbc 100644
--- a/base/files/file_path_watcher.h
+++ b/base/files/file_path_watcher.h
@@ -62,9 +62,8 @@
       return task_runner_;
     }
 
-    void set_task_runner(
-        scoped_refptr<base::SingleThreadTaskRunner> task_runner) {
-      task_runner_ = task_runner.Pass();
+    void set_task_runner(scoped_refptr<base::SingleThreadTaskRunner> runner) {
+      task_runner_ = std::move(runner);
     }
 
     // Must be called before the PlatformDelegate is deleted.