[TaskScheduler] Remove temporary forwarding headers and mass migrate users

When this CL is approved I will rebase it on top of tree and mass
migrate all callers in a new patch set (TBR'ed change).

[email protected] (for mass migration of existing callers)

Bug: 867421
Change-Id: I41092bbc4824964ee047e0bf53e972c8f6e896a4
Reviewed-on: https://chromium-review.googlesource.com/1161116
Commit-Queue: Gabriel Charette <[email protected]>
Reviewed-by: Gabriel Charette <[email protected]>
Reviewed-by: Sami Kyöstilä <[email protected]>
Cr-Commit-Position: refs/heads/master@{#580845}
diff --git a/content/shell/browser/shell_download_manager_delegate.cc b/content/shell/browser/shell_download_manager_delegate.cc
index c8620ed..45d196c9 100644
--- a/content/shell/browser/shell_download_manager_delegate.cc
+++ b/content/shell/browser/shell_download_manager_delegate.cc
@@ -18,7 +18,7 @@
 #include "base/macros.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
-#include "base/task/post_task_forward.h"
+#include "base/task/post_task.h"
 #include "build/build_config.h"
 #include "content/public/browser/browser_context.h"
 #include "content/public/browser/browser_thread.h"