[base] Migrate away from base::PostTask in virtual_keyboard_policy_uitest_win.cc

base::PostTask with no traits implicitly posted to base::ThreadPool.

This isn't necessary here. The correct semantics would have been to
post to ThreadTaskRunnerHandle::Get(). But even that seems unnecessary
as RunLoop::Quit() can be invoked directly in this context.
Assuming the test doesn't need to let pending tasks run before
quitting the loop.

This change is blocking https://chromium-review.googlesource.com/c/chromium/src/+/2225541

Bug: 968047, 1026641
Change-Id: I6caea1ee7c7f3089ebc8a7786a4755eb784cac80
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2228118Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Anupam Snigdha <snianu@microsoft.com>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774668}

chrome/browser/virtual_keyboard_policy_uitest_win.cc

@@ -7,7 +7,6 @@
 #include "base/macros.h"
 #include "base/run_loop.h"
 #include "base/strings/utf_string_conversions.h"
-#include "base/task/post_task.h"
 #include "base/win/windows_version.h"
 #include "build/build_config.h"
 #include "chrome/browser/ui/browser.h"
@@ -61,7 +60,7 @@ class TextInputManagerObserverBase {
 
   void OnSuccess() {
     success_ = true;
-    base::PostTask(FROM_HERE, run_loop.QuitClosure());
+    run_loop.Quit();
 
     // By deleting |tester_| we make sure that the internal observer used in
     // content/ is removed from the observer list of TextInputManager.