Revert of Use TaskScheduler instead of SequencedWorkerPool in snapshot_cache.mm.

ios/chrome/browser/snapshots/snapshot_cache.mm

Index: ios/chrome/browser/snapshots/snapshot_cache.mm
diff --git a/ios/chrome/browser/snapshots/snapshot_cache.mm b/ios/chrome/browser/snapshots/snapshot_cache.mm
index f170a1b3dad5c6a91931aed7d07d260716658fe3..a2174949b9af2fa022eb02952cddf29d9582a54a 100644
--- a/ios/chrome/browser/snapshots/snapshot_cache.mm
+++ b/ios/chrome/browser/snapshots/snapshot_cache.mm
@@ -18,7 +18,6 @@
 #include "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/task_runner_util.h"
-#include "base/task_scheduler/post_task.h"
 #include "base/threading/thread_restrictions.h"
 #include "ios/chrome/browser/experimental_flags.h"
 #import "ios/chrome/browser/snapshots/lru_cache.h"
@@ -572,10 +571,9 @@
     }
   }
 
-  base::PostTaskWithTraits(
-      FROM_HERE, {base::MayBlock(), base::TaskPriority::USER_VISIBLE},
-      base::BindOnce(&ConvertAndSaveGreyImage, colorImagePath, greyImagePath,
-                     backgroundingColorImage_));
+  web::WebThread::PostBlockingPoolTask(
+      FROM_HERE, base::Bind(&ConvertAndSaveGreyImage, colorImagePath,
+                            greyImagePath, backgroundingColorImage_));
 }
 
 @end