[ThreadPool] Add missing static keyword on new base::ThreadPool::PostTaskAndReplyWithResult API

TBR=fdoray@chromium.org

Bug: 1026641
Change-Id: Id22f4e3e66ce2127e4cec8a9ceddcf63c107abbf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2026311Reviewed-by: Gabriel Charette <gab@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#736218}

base/task/thread_pool.h

@@ -172,10 +172,11 @@ class BASE_EXPORT ThreadPool {
             typename TaskReturnType,
             typename ReplyArgType,
             typename = EnableIfIsBaseCallback<CallbackType>>
-  bool PostTaskAndReplyWithResult(const Location& from_here,
-                                  const TaskTraits& traits,
-                                  CallbackType<TaskReturnType()> task,
-                                  CallbackType<void(ReplyArgType)> reply) {
+  static bool PostTaskAndReplyWithResult(
+      const Location& from_here,
+      const TaskTraits& traits,
+      CallbackType<TaskReturnType()> task,
+      CallbackType<void(ReplyArgType)> reply) {
     auto* result = new std::unique_ptr<TaskReturnType>();
     return PostTaskAndReply(
         from_here, traits,