IWYU for callback_helpers.h

Prereq for https://chromium-review.googlesource.com/c/chromium/src/+/2773408
as we previously had
task_traits.h=>thread_pool.h=>callback_helpers.h

Users that should be including thread_pool.h explicitly did so in
https://chromium-review.googlesource.com/c/chromium/src/+/2775891

These are the remaining users of types in callback_helpers.h that
weren't properly IWYU. e.g.:
../../media/video/software_video_encoder_test.cc:92:54: error: no member named 'NullCallback' in namespace 'base'
std::move(output_cb), base::NullCallback());

Script:

def Fix(file_path):
  content = refactor_lib.ReadFile(file_path)

  # Assume fwd-decls are correct in first pass.
  if 'class ScopedClosureRunner;' in content:
    return False

  # Using base:: prefix ensures we don't match fwd-decls and other
  # things. Will require a few fixups for missing includes in //base
  # proper. Complex prefix in regex attempts to skip comments.
  matches = re.compile(
      r'(\n *[^/\n][^/\n][^/\n]*'
      r'(base::ScopedClosureRunner|base::NullCallback|base::DoNothing)'
      r'\b[^*])',
      re.DOTALL).findall(content)

  if not matches:
    return False

  updated_content = refactor_lib.AddInclude(file_path, content,
                                            "base/callback_helpers.h")

  if updated_content == content:
    return False

  # Write updated file
  refactor_lib.WriteFile(file_path, updated_content)

  return True

Bug: 1026641
Change-Id: Ic7cfec226f1a13b05f4244d5ffcdd2ad8c4e4c3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2774781
Commit-Queue: Gabriel Charette <[email protected]>
Reviewed-by: François Doray <[email protected]>
Reviewed-by: Lei Zhang <[email protected]>
Owners-Override: François Doray <[email protected]>
Owners-Override: Lei Zhang <[email protected]>
Cr-Commit-Position: refs/heads/master@{#865177}
diff --git a/chrome/browser/ui/ash/clipboard_util.cc b/chrome/browser/ui/ash/clipboard_util.cc
index b2dc6e0..699749e 100644
--- a/chrome/browser/ui/ash/clipboard_util.cc
+++ b/chrome/browser/ui/ash/clipboard_util.cc
@@ -10,6 +10,7 @@
 #include "ash/public/cpp/clipboard_history_controller.h"
 #include "base/base64.h"
 #include "base/callback.h"
+#include "base/callback_helpers.h"
 #include "base/files/file_util.h"
 #include "base/memory/ref_counted_memory.h"
 #include "base/memory/scoped_refptr.h"