[base] Make PostTaskAndReply destination explicit in /extensions/browser/api/crash_report_private

Task APIs v3 will all have an explicit destination. In the past
"default traits" meant ThreadPool. This CL is thus a no-op.

These changes are required to phase out task APIs v2 (post_task.h)
Design doc: https://docs.google.com/document/d/1tssusPykvx3g0gvbvU4HxGyn3MjJlIylnsH13-Tv6s4/edit

This CL was uploaded by git cl split.

R=ortuno@chromium.org

Bug: 1026641, 968047
Change-Id: I6971ac85ba55e6960fa74e6dbb078a1a30467e27
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2219033
Auto-Submit: Gabriel Charette <gab@chromium.org>
Commit-Queue: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Reviewed-by: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773580}

extensions/browser/api/crash_report_private/crash_report_private_api.cc

@@ -7,7 +7,6 @@
 #include "base/strings/strcat.h"
 #include "base/strings/stringprintf.h"
 #include "base/system/sys_info.h"
-#include "base/task/post_task.h"
 #include "base/task/task_traits.h"
 #include "base/task/thread_pool.h"
 #include "base/time/default_clock.h"
@@ -216,8 +215,8 @@ ExtensionFunction::ResponseAction CrashReportPrivateReportErrorFunction::Run() {
 
   // Consent checking may be blocking, so do it on a separate thread to avoid
   // blocking the UI thread.
-  PostTaskAndReplyWithResult(
-      FROM_HERE, {base::ThreadPool(), base::MayBlock()},
+  base::ThreadPool::PostTaskAndReplyWithResult(
+      FROM_HERE, {base::MayBlock()},
       base::BindOnce(&crash_reporter::GetClientCollectStatsConsent),
       base::BindOnce(
           &CrashReportPrivateReportErrorFunction::OnConsentCheckCompleted, this,
@@ -240,7 +239,7 @@ void CrashReportPrivateReportErrorFunction::OnConsentCheckCompleted(
           ->GetURLLoaderFactoryForBrowserProcess();
 
   // Don't anonymize the report on the UI thread as it can take some time.
-  PostTaskAndReplyWithResult(
+  base::ThreadPool::PostTaskAndReplyWithResult(
       FROM_HERE, base::BindOnce(&AnonymizeErrorMessage, info.message),
       base::BindOnce(
           &ReportJavaScriptError, std::move(loader_factory), std::move(info),